Green’s Dictionary of Slang

d.c.m. n.

In phrases

get a d.c.m. (v.) [abbr. don’t come Monday]

(Aus./US) to be dismissed from one’s job.

1985		F. Deford Sports Illus. June 🌐 [E]ven if it meant that maybe when they went back to the mills in Pittsburgh they'd be handed a DCM. A DCM is a Don't Come Monday, the pink slip.
1999		G. Seal Lingo 155: Other terms for losing one’s job include to [...] get a dcm, that is don’t come monday.