I'll re-post here what I'd posted on the American Dialect Society listserv, FYI.


As I've been saying all along, "BLT" was the popular abbreviation for the
Chicago Tribune "Line o' Type" columnist Bert L. Taylor, and that we'd
probably find the "BLT" sandwich earliest in the Chicago Tribune.
Here goes:

(PROQUEST HISTORICAL NEWSPAPERS)
A LINE O' TYPE OR TWO; SIGHTS OF CHICAGO, 1868.
CHARLES COLLINS. Chicago Daily Tribune (1872-1963). Chicago, Ill.: Nov 10,
1944. p. 18 (1 page):
B. L. T., according to Transatlantic Quiz, is the abbreviation for bacon,
lettuce, and tomato sandwiches.
Quizzicuss