Green’s Dictionary of Slang

(US) organized crime, almost always US Mafia.

1975		E. Torres Carlito’s Way 142: ‘[T]hey’re going to close the door on me. Wops don’t make parole—right away they stamp us O.C. or mafia’.
1994		P. Blauner Casino Moon 128: ‘Well now, see, you’re in a situation [...] You’re a known o.c. associate with outstanding warrants and you’re driving around with that shit in your car’.
2019		D. Winslow Border [ebook] [T]he word would get around the northeast OC community that a New York detective was off the leash, gambling heavy, losing heavy, drinking heavy.