A “hechsher” (also sometimes spelled “hechscher,” but seldom “hecksher”) is a certification marking on products (usually foods, but also kitchen cleansers, soaps and other items) that they’re “kosher” under the Jewish dietary laws. The Orthodox Union of New York City states that its “OU” (registered in 1925) is the world’s best known kosher trademark.
   
The word “hechsher” is Hebrew and is cited in English language publications by at least 1918.
   
 
Wikipedia: Hechsher
A hechsher (IPA: /hɛxʃəʁ/, הכשר Hebrew: “kosher approval” , plural: hechsherim) is the special certification marking found on the packages of products (usually foods) that have been certified as kosher (meaning “fit” for consumption). In Halakha (Jewish law), the dietary laws of kashrut specify food items that may be eaten and others that are prohibited as set out in the commandments of the Torah. Observant Jews generally will only eat permitted foods. To assist Jewish consumers, rabbinic authorities produce and regulate their own hechsherim. It is usually Orthodox rabbis who assume the jobs of mashgichim (singular: mashgiach, “supervisor”). This means that they will “supervise” the products and processes that manufacture kosher food to ensure compliance with the required standards. The mashgiach will allow the manufacturer to apply a hechsher to the packaging of the product only if found to contain only kosher ingredients and produced in accordance with Halakha. The rabbi may also apply additional words or letters after the hechsher to denote whether the product contains meat (often denoted “Meat”), dairy (D or Dairy), neither meat nor dairy (Pareve), whether the product is Kosher for Passover because it contains no chametz (P), whether the product is pas yisroel (bread baked at least in part by a Jew), cholov yisroel (any dairy products came from Jewish owned farms), or whether the product is yoshon (lit. “old”: all grain contents took root before the previous Passover).
 
Specific authorities
In America, one of the best known hechsher symbols is the “OU” of the Orthodox Union based in New York City in the United States. Outside of the United States, they are less well known. They employ hundreds of rabbis as mashgichim and are generally accepted.
   
Hechshers.info
Links to web-sites about kashrut and hechshers
     
OU—The world’s best known kosher trademark
An ‘OU’ symbol indicates
The product is Kosher (but not necessarily Kosher for Passover).
The product contains neither dairy nor meat, nor any dairy or meat derivatives.
The product was not made on equipment also used for making dairy products.
The product was not made on equipment also used for making meat products.
In Kosher Lexicon, such a product is called ‘Pareve’ or sometime ‘Parve’
 
Equipment, pots, dishes, cutlery, etc that has not been used for dairy and not for meat is also called ‘Pareve Equipment’, ‘Pareve Pots’ etc.
 
Pareve foods may be eaten with milk or with meat.
Pareve foods may be re-cooked in any Kosher equipment be it meat or be it dairy.
 
An ‘OU-D’ symbol indicates:
The product is a Kosher dairy product (but not necessarily Kosher for Passover),
The product contains a dairy ingredient or a dairy derivative.
Alternatively, the product, while not containing dairy ingredients itself, was made on equipment also used for making dairy products.
Kosher laws do not permit a dairy food to eaten or cooked with meat or with foods made with meat ingredients. 
 
Kosher laws dictate that if one has just eaten meat, one must wait a prescribed time before being allowed to eat a product marked OU-D.
 
An OU-D product may not be reheated on or with any equipment, pot, pan, dishes, cutlery that was used for meat.
An OU-D product that had been reheated on or with any equipment, pot, pan, dishes, cutlery that was used for meat, would possibly make both the product and the utensil not Kosher.
 
An ‘OU-M’ symbol or an OU-Glatt symbol indicates:
 
The product is Kosher meat or a product with meat ingredients or a derivative of meat (but not necessarily Kosher for Passover)
 
Alternatively, the product, while not containing meat ingredients itself, was made on equipment also used for making meat products.
Kosher laws do not permit meat or a food with meat ingredients to be eaten with or cooked with dairy or with foods made with dairy ingredients. 
 
Kosher laws dictate that if one has just eaten dairy, one does not have to wait a prescribed time before being allowed to eat a product marked OU-M or OU-Glatt.
Though it is suggested to either rinse the mouth or have a half hour wait between the dairy food and meat.
 
An OU-M or an OU-Glatt product may not be reheated on or with any equipment, pot, pan, dishes, cutlery that was used for dairy.
 
An OU-M or OU-Glatt product that had been reheated on or with any equipment, pot, pan, dishes, cutlery that was used for dairy, would possibly make both the product and the utensil not Kosher.
 
An ‘OU-F’ symbol indicates
The product is a Kosher product with fish ingredients (but not necessarily Kosher for Passover)
 
The product should NOT be eaten with nor cooked with meat or with foods made with meat ingredients.

It is permitted to eat an OU-F product right before or right after having meat.

OU-F products may be eaten and cooked together with Dairy foods.
 
While Kosher law allows cooking an OU-F product on meat equipment, it has become a custom to have a separate pot for cooking or reheating fish
 
Please Note the following: On products where the fish content is recognizable – either because the product is a fish or the product name includes the name of a fish (i.e. Tuna Salad) the designation might be a plain OU, as well as it might be OU-F.
 
In either case, Kosher laws nix on eating fish and meat together.
 
It is in situations where the fish ingredient is not obvious, that the OU-F becomes important.
 
In products containing a fish ingredient, as opposed to products containing a dairy or a meat ingredient, the amount of the fish ingredient in relation to the other ingredients in the product is the determining factor whether to label the product OU-F or not.  If the ratio of the quantity of other ingredients in the product to the fish ingredient is less than 60 to 1, the product is labeled OU-F.  If the other ingredients are equal or greater than the Kosher mandated (60 to 1) ratio, Kosher law considers the fish ingredient to have dissipated in the other ingredient and the ‘F’ will not be assigned to the product.
 
This will explain why some OU certified Worcestershire sauces containing anchovies, are assigned OU-F and other brands are assigned OU.  In the latter case, it is because the quantity of the anchovies in the product was small so it became dissipated.
 
An ‘OU-P’ indicates
The product is Pareve and Kosher for Passover as well as for year-around.
 
An OU-D-P indicates
Product is dairy and Kosher for Passover as well as for all year round.
 
An OU-M-P or an OU-Glatt-P indicates
Product is meat and Kosher for Passover as well as for all year round.
 
An OU-F-P indicates
Product contains Fish and Kosher for Passover as well as for all year round.
 
Google Books
Yohale Sarah
Containing Religious Duties of the Daughters of Israel and Moral Helps
By Rabbi Abraham E. Hirschowitz
Fourth Edition
New York, NY: Hebrew Publishing Co.
1918 (Copyright 1902-1913-1918)
Pg. xxxv:
One more point I would like to make clear. Here in America we spend so much money in our attempt to make our Passover complete; we buy matza, wine, brandy, sugar, etc., that is marked by a “Hecksher” (sic) and think in our ignorance that we have done our duty. it is not sufficient that we look for the “Hechsher” and even find it signed by the proper authority. It is encumbent upon every buyer to know the character and reputation of the person using that “hechsher.” The man we deal with for Kosher meat, or for food for Passover, must be one who keeps the Sabbath and has the reputation of a pious Israelite.
     
Google Books
The Jewish Communal Register of New York City 1917-1918
Second Edition
Edited and Published by the Kehillah (Jewish Community) of New York City0
356 Second Avenue
New York City
1918
Pg. 289:
The committee also watched that the unleavened bread, the wine and liquors, as well as all other food articles used for Passover shall be free from any suspicion of “Chomets” or leaven, requiring that every article marketed shall have the “Hechscher” of a recognized rabbi. 
   
29 October 1920, Jewish Daily News (NY), pg. 20:
But why did this “Vaad Hakashruth” only issue a hechsher for Meyer London? What about Morris Hillquit, the “genosse of genossen?” And what about the other candidates of the “kleisel?” Are we to assume that the “Vaad Hakashruth” issued a blanket hechsher, the names to be filled in in the officer of the “Forward” over the ready signature of Rabbi Yudelewitz and Rabbi Margolin?
 
Pittsburgh Jewish Newspaper Project
21 April 1922, The Jewish Criterion, pg. 7, col. 2:
“This Hagada is strictly Kosher. It has a Hechsher of the New York City Rabbi; will cost you only one dollar. It’s a bargain.”
 
Pittsburgh Jewish Newspaper Project
4 April 1924, The Jewish Criterion, pg. 17, col. 4:
At the meeting held last Monday night the Rabbis, after a heated discussion, agreed with Rabbi Sivitz’s motion that although some of the Rabbis are altogether opposed to the issuing of “Passover Hechsheirim” (permits), because of the strictness ofthe Passover lawws, but taking into consideration the public’s welfare, and that there are certain articles such as milk and other articles of this character which the public cannot do without, permits shall be issued to the firms of Rieck-McJunkin Co. and Hermes Milk Co. Said permits only shall be issued after the Rabbis will have visited the farms and inspected the milking and shipping conditions, and also have instructed the farmers as to what the cattle shall be fed on Passover week. The following Rabbis agreed to give a day this week and go out to the farms: Sivitz, Kochin, Leiter, Freidman and Rabbi Levy from McKeesport. Jewish housewives are urged to look for the “Hechsher” on every bottle of milk.
     
Kosher Americans
By Joseph D. Rosenberg
Atlantic City, NJ: Associated Publishers Company
1929
Pg. 321:
APPENDIX
Number indicates page where word or phrase is set forth in this narrative.
YIDDISH   TRANSLATION
(...)
Hechscher…stamp of approval…20
   
Pittsburgh Jewish Newspaper Project
22 April 1932, The Jewish Criterion, pg. 54, col. 1:
Horowitz-Maragareten Passover products carry three rabbis’ “hechscher.”
 
August 1933, Orthodox Union, pg. 4, col. 1:
Up to about nine years ago the Kashruth of articles labeled as “Kosher” were frequently questioned because many a “Hechsher” was obtained for financial consideration.
 
Google Books
History of Brooklyn Jewry
By Samuel Philip Abelow
Brooklyn, NY: Scheba Publishing Company
1937
Pg. 289:
The historical “hechsher” on this soap by Rabbi Isaac Elchanan was also a high tribute to Israel Rokeach himself.
     
21 April 1948, New York (NY) Times, pg. 30 ad:
Look for the Rabbinical certificate on label, and special tamper-proof “Hechsher” on bottle-cap.
(Horowitz Margareten Kosher Passover Wines—ed.)
   
The Jewish Daily Forward
H-e-c-h-s-h-e-r
By Forward Staff
Published June 09, 2006, issue of June 09, 2006.
Saryn Hooks didn’t end up winning the 79th annual Scripps National Spelling Bee last week in Washington. But before finishing third, the 14-year-old girl from Taylorsville, N.C., managed to stump the judges on the word “hechsher” — the endorsement signifying that something has been certified kosher.
 
The judges disqualified her, saying that the correct spelling was “hechscher.” But family members of other contestants, checking on their laptops, quickly reported that it was the judges who, in fact, were offering the treyf spelling.
 
Hooks was reinstated, but she was no match for “icteritious” (look it up).
     
(Trademark)
Word Mark OU
Goods and Services IC A . US A . G & S: PACKAGING MATERIALS AND WRAPS; BROILING AND BAKING PANS; FLAVORS, EXTRACTS AND FOOD COLORINGS; WINE, LIQUEURS, AND CORDIALS; NON-ALCOHOLIC BEVERAGES; SPICES AND SEASONINGS; AND SOAPS. FIRST USE: 19250000. FIRST USE IN COMMERCE: 19250000
IC B . US B . G & S: HOTEL CAMP RESTAURANT AND CATERING SERVICES, FOOD SERVICES IN HOSPITALS AND OTHER INSTITUTIONS AND FOR TRAVELLERS ON AIRLINES. FIRST USE: 19610000. FIRST USE IN COMMERCE: 19610000
Mark Drawing Code (5) WORDS, LETTERS, AND/OR NUMBERS IN STYLIZED FORM
Serial Number 73130761
Filing Date June 17, 1977
Current Filing Basis 1A
Original Filing Basis 1A
Change In Registration CHANGE IN REGISTRATION HAS OCCURRED
Registration Number 1087891
Registration Date March 21, 1978
Owner (REGISTRANT) UNION OF ORTHODOX JEWISH CONGREGATIONS OF AMERICA CORPORATION NEW YORK ELEVEN BROADWAY NEW YORK NEW YORK 10004
Attorney of Record DAVID O. JOHANSON
Prior Registrations 0636593
Type of Mark CERTIFICATION MARK
Register PRINCIPAL
Affidavit Text SECT 15. SECT 8 (6-YR). SECTION 8(10-YR) 20080401.
Renewal 2ND RENEWAL 20080401
Other Data THE CERTIFICATION MARK AS USED BY PERSONS AUTHORIZED BY APPLICANT CERTIFIES THAT THE PRODUCTION OF SAID GOODS AND THAT THE RENDERING OF SAID SERVICES HAS BEEN SUPERVISED BY THE RABBINICAL SUPERVISORS OF THE APPLICANT, UNDER THE DIRECTION OF HISTADRUTH HORABONIM DE AMERICA-RABBINICA COUNCIL OF AMERICA, INC.
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