“Never sell on strike news” (or “Don’t sell on strike news”) is one of Wall Street’s oldest adages. A strike often fails or is settled quickly; panic selling on strike news is often a poor investment strategy.
 
Addison Cammack (1826-1901) was known as “Ursa Major” because he was a famous Wall Street “bear.” His policy of “I don’t sell stocks on a strike” was cited in print in August 1890, but had become part of Cammack’s trading philosophy in the 1880s. The modern forms of the saying—“don’t sell on strike news” and “never sell on strike news”—have been cited in print since at least 1921.
 
   
17 August 1890, New York (NY) Times, “The Financial World,” pg. 5:
Mr. Cammack said he did not sell stocks on a strike, and whatever selling he was doing was on the crop damage.
   
31 August 1890, New York (NY) Times, “The Financial World,” pg. 5:
As to the labor troubles, they are local and ephemeral, occupying much space in the papers, but having no proportionate importance in respect to the stock market. Mr. Cammack is a sagacious old bear operator, and his dictum is: “I don’t sell stocks on a strike.”
 
18 August 1892, Wall Street Daily News (New York, NY), “On Deck,” pg. 2:
Cammack hurried down from Saratoga on Tuesday night and was on the street bright and early yesterday morning. His friends say that he is not selling stocks on the switchmens’ strike at Buffalo, as he was taught about a dozen years ago “that it is not safe to sell stocks on a strike” and the lesson was a very expensive one.
 
7 February 1897, New York (NY) Times, pg. 4:
MR. CAMMACK’S RETIREMENT
Conflicting Impressions Have Been Left
in Wall Street by the Aged
Operator.
WAS KNOWN AS “URSA MAJOR.”
His Bear Dealings Gave Him That Nickname—To Casual Acquaint-
ances He Was Gruff and Repel-
lant, To His Cronies He
Was Pleasant.
Few stock brokers who have attracted attention as daring, brilliant, and successful operators have retired to private life after a long career on “the Street” and left such varying impressions of their character as Addison Cammack.
 
8 July 1897, New York (NY) Times, pg. 4:
DON’T SELL ON STRIKES.
A Wall Street observer calls attention to the axiom of Mr. Cammack, the veteran bear operator, which is, never to sell stocks on a strike. it is all right to sell them on the rumors and earliest stage of a strike, but never on the full-fledged strike itself. Experience shows that strikes fail or are settled up, in either of which events the market gets a fresh upward impetus.
 
Google News Archive
16 September 1900, Troy (NY) Northern Budget, “Financial Outlook,” pg. 19, col. 4:
Wall street at large seems to have learned the rule which was always referred to by Addison Cammack, in his day one of the most renowned of bear operators, that strike or labor disturbances are poor reasons for selling stocks short.
     
6 February 1901, New York (NY) Times, pg. 9:
ADDISON CAMMACK DEAD
One-Time Bear Leader of Wall
Street passes Away in This City.
Gruff Broker Who Won Fame and For-
tune by His Daring Coups Began
Life as Office Boy.
Addison Cammack, the retired Wall Street stock broker and operator, died yesterday morning at his city home, 31 West Forty-ninth Street, in his seventy-fifth year. he had for several months suffered from Bright’s disease.
 
Addison Cammack was for twenty years the leader of the Wall Street bear clique, and his successor was James R. Keene, until the latter returned from Europe and got into the bull swim that was brought about by the election for a second term of president McKinley. Familiarly termed “Cam” and “Ursa Major,” his personality was interesting because of his stature and brawn, and to those to whom he unbent—they were few—he became cherished.
 
9 April 1921, Philadelphia (PA) Inquirer, “Stocks sag on absence of demand,” pg. 16:
Moreover, they were mindful of the old saying, “don’t sell on strike news,” the theory of which is that strikes invariably are either settled or broken, sometimes very unexpectedly, thereby suddenly eliminating an unfavorable factor.
     
18 October 1921, New York (NY) Times, “Topics in Wall Street,” pg. 30:
“Never Sell on Strike News.”
Away back in Wall Street’s dark ages, some one coined a phrase that has been accepted as gospel since that time. It was this: “Never sell stocks on strike news.” It was heard up and down Wall Street again yesterday, and probably had much to do with the volumes of shares offered for sale. One has to go no further back than the “outlaw” railroad strike or the attempt to tie up the plants of the United States Steel Corporation to find a measure of truth in the axiom.
 
Google Books
Investment In This Changing World
By Otto von Mering
Boston, MA: Barron’s Pub. Co.
1950
Pg. 117:
“Never Sell on Strike News” Specifically, the idea that temporary bad news is not a selling signal has found expression in the old stock exchange slogan, “Never sell on strike news.”
 
Google Books
The Stock Market
By George Leland Leffler
New York, NY: Ronald Press Co.
1951
Pg. 47:
This tendency has resulted in many Wall Street axioms ; for example, “Never sell on strike news.”
   
Google Books
The Anatomy of Wall Street;
A guide for the serious investor
By Charles James Rolo and George J Nelson
Philadelphia, PA: Lippincott
1968
Pg. 4:
This is implicit in maxims enshrined in the folklore of Wall Street: “Never sell on strike news,” or “Sell when the good news is out.”