Green’s Dictionary of Slang

(US Und.) a suspended sentence.

1950		Goldin et al. DAUL 206/2: S. S. A suspension of sentence by the court.
1958		Murtagh & Harris Cast the First Stone 217: I just think I ought to get a S.S. [...] I’m tired of going to jail.
1966		J. Mills Panic in Needle Park (1971) 166: Remember I said in the Automat that when a junkie gets busted he rats on a couple of connections to get an SS—a suspended sentence?
1971		E.E. Landy Underground Dict. (1972).