Yours, Etc.: Origins and Uses of 8 Sign-Offs
1963, noun and verb, U.S. slang, a carnival term, of unknown origin. Perhaps related to 19c. British slang scamp "cheater, swindler" (see scamp (n.)).
A swindler or hustler
what's the scam
[origin unknown; perhaps related to early 1800s British scamp, ''cheater, swindler'']