“Protect your bagels. Put lox on them”

New York Pastrami Factory (333 East 23rd Street in Manhattan) was cited in March 1983 for this jocular sign in a window:
 
“Protect your bagels. Put lox on them.”
 
The line (a pun on the word “locks”) has been frequently reprinted.
 
   
Google Books
7 March 1983, New York magazine, pg. 111, col. 2 ad:
Protect your bagels. Put lox on them.
(...)
New York Pastrami Factory
333 East 23rd St.
(Between 1st and 2nd Ave.)
   
New York (NY) Times
METROPOLITAN DIARY
By Glenn Collins
Published: March 23, 1983
(...)
Deborah Slom saw this sign in the window of the Pastrami Factory on East 23d Street in Manhattan: ‘‘Protect Your Bagels: Put Lox on Them.’‘
 
Google Books
Deli:
101 New York-style deli dishes, from chopped liver to cheesecake
By Sue Kreitzman
New York, NY: Harmony Books
1985
Pg. 79:
“Protect your bagels— put lox on them!”
Sign, Goldberg and Son’s
Bagel Bakery and Deli
Atlanta, 1984
 
Google Books
The Reader’s Digest
Volume 126, Issues 753-758
1985
Pg. 42:
SIGN IN THE WINDOW of a Manhattan eatery: “Protect Your Bagels. Put Lox on Them.” — Deborah Slom, quoted by Glenn Collins in New YorkTimes
 
Google Books
Get Thee to a Punnery
By Richard Lederer
New York, NY: Dell Publishing
1989
Pg. 15:
Protect your bagels. Put lox on them.
 
Google News Archive
23 October 1992, Milwaukee (WI) Sentinel, “Putting a new peg on those holes in the golf course” by Alex Thien, pg. 3C, col. 3:
Louise O’Brien says the sign is in a deli: “Protect your bagels. Put lox on them.”
 
Twitter
Einstein Bros.
‏@EinsteinBros
Weekend Funnies: How do you protect your bagels?
Put lox on them! ha! http://fb.me/3A1sGe4uv
10:30 AM - 11 Jan 2014