Wordorigins.org

The brand name Spam, used for a potted meat product made by the Hormel Corporation, is a blend of spiced + ham. It was trademarked in 1937 and appears in the Official Gazette of the US Patent office on 26 October of that year:

Geo. A. Hormel & Company, Austin, Minn...Spam...For Canned Meats—Namely, Spiced Ham. Claims use since May 11, 1937.