“Register Communists, not firearms” ia an anti-gun control slogan that has been printed on many gift items, such as bumper stickers and coffee mugs. “I say register Communists, not guns” was written in a letter to the editor of an Arizona newspaper in December 1964. “Register Communists, Not Firearms” has been cited in print since at least May 1965, when it was associated with the John Birch Society.
   
     
Google News Archive
16 December 1964, Prescott (AZ) Evening Courier, Letters To The Editor, pg. 4, col. 3:
Have you not heard that they want to make the private citizen register his guns? The day will come when he must do so! When that has been achieved it will be a simple matter to take them away from him! I say register Communists, not guns!
(Letter by Duane Smith—ed.)
 
6 May 1965, The News (Van Nuys, CA), “Anti-Defamation League Warning Cites ‘Front Groups’ Inspired by John Birch Society When Avoiding Identity,” pg. 10A, cols. 5-6:
He charged that other Birch inspired front-groups operating out of post-office boxes, are the “Student Committee for Intellectual Freedom,” Inglewood; “Citizens for Support of Law and Order,” La Puente; “The Committee to Mourn Our President’s Violent Death.” Los Angeles and Gardena. whose “avowed purpose,” Senn reported, is to register Communists, not firearms.
 
28 July 1965, Richardson (TX) Digest, “Coffee Talk” by Marion Taylor, pg. 1, col. 3:
NEW CAR STICKERS—on RON CAMERON’S car, Register Communists, Not Firearms; and on BOB BILLINGS’ auto, Bomb the Ban, and Go To College and Learn to Riot.
     
12 September 1965, Boston (MA) Globe, “Who Should Have a Gun?” by Drew Pearson, pg. ‎A3:
The NRA plastered Camp Perry with slogans opposing the Dodd Bill and handed out thousands of bumper stickers proclaiming “Fight Crime Not Sportsmen,” “Beware of Gun Laws” and “Register Communists Not Firearms.”
 
Google Books
Language for Writing
By Robert S. Newman
Belmont, CA Dickenson Pub. Co.
1967
Pg. 27:
With this in mind, take any one of the slogans below and discuss the possibility that two people might mistakenly assume that they were disagreeing at the level of of truth or falsity rather than at the level of the basic meaning of the terms: Better Red than Dead; Register Communists, not Firearms; Make Love not War; Support Your Local Police; Support Your Supreme Court: It Serves and Protects You.
 
14 October 1969, Greensboro (NC) Record, “The Hot Line,” pg. 1, col. 1:
Rare Stickers
Q. Last week I noticed a bumper sticker sayong “Register Communists Not Firearms.” I am in full agreement with this and wonder where I can get one. C.L.
A. Just go by the Wallace campagn headquarters, 110 West Market St. These particular stickers are rare as hens’ teeth, but one has been set aside especially for you.
 
Google Books
Nixonland:
The Rise of a President and the Fracturing of America
By Rick Perlstein
New York, NY: Scribner
2008
Pg. 662:
By their bumper stickers, you could know them: I FIGHT POVERTY; I WORK; GOD BLESS AMERICA; POW’S NEVER HAVE A NICE DAY; REGISTER COMMUNISTS, NOT FIREARMS.