Green’s Dictionary of Slang

(US und.) a coded introductory question which is used to established which branch of the US Mafia a given individual is linked to.

1991

B. McCarthy Vice Cop 218: ‘“Who are you with?” Just like that. That question is the classic mob introduction. It takes the place of “How do you do?” Then, before I even have a chance to answer, he says, “My name is Angelo. From now on you’re with me. Anybody bothers you, just say you are with me and I am Carmine-by-the-Bay”’.