message, n. — Green’s Dictionary of Slang

message n.

1. (US und.) an arrest warrant.

1918

Jackson Dly News (MS) 1 Apr. 7/3: Crook Chatter [...] ‘A warrant for arrest is a “message” or “reader”’.

2. (UK Und.) instructions passed on among criminals.

1989

(con. 1950s–60s) in G. Tremlett Little Legs 195: message the euphemism for instructions given by one criminal to another suggesting that a third party be wounded or even killed, as in ‘give Johnny the message’.

SE in slang uses

In phrases

get the message (v.) (also get the memo) [orig. jazz use, but now general]

to appreciate, to understand.

1965		A. James America’s Homosexual Underground 71: He [...] looked down at the bulge in his pants. I got the message.
1967		P. Thomas Down These Mean Streets (1970) 263: Claude got the message and peddle his ass elsewhere.
1977		S. Berkoff East in Decadence and Other Plays (1985) 69: I stood there clocking it, wanting her to get the message.
1981		H. Gould Fort Apache, The Bronx 75: But Dugan didn’t get the message.
2003		Eble Campus Sl. Nov. 3: get the memo – do the acceptable thing. Commenting on a student talking in class after the teacher had asked students to stop: Apparently Glenn didn’t get the memo.