Green’s Dictionary of Slang

1. to rob in the street, to garrotte, to ‘mug’; thus n. hanger-up.

1872		E. Crapsey Nether Side of NY 23: [T]hose desperate thieves the police style ‘hangers-up,’ who steal upon a man in some private place, bind him hand and foot, and after robbing him leisurely and effectually, go away.
1873		Sl. Dict. 188: Hang up to rob with violence, to garrotte. Most likely from throttling associations in connexion with the practice of garrotting.
1887		Cincinnati Enquirer (OH) 24 Dec. 12/3: [pic. caption] Hanging a Man Up.
1895		Crowe Aus. Sl. Dict. 35: Hang Up, to garotte.
1895		Mirror of Life 13 Apr. 6/1: [T]he [...] then editor of the Sporting Life, when entering Tattersall's, was about, in professional language, to be ‘hung up’ for his ‘red lot’ [etc] .
1973		(ref. to 1890s) ‘Gloss. of Larrikin Terms’ in J. Murray Larrikins 203: hang up: garotte.

2. (US prison) to commit suicide by hanging.

1950		Goldin et al. DAUL 91/1: Hang up [...] To commit suicide by hanging. That dude [..] is blowing his top (losing his sanity). He’ll hang up one of these nights.
1994		P. Baker Blood Posse 346: I hope you ain’t hanging up in there.
2023		Rayman & Blau Riker’s 11: Make sure nobody escapes and nobody hangs up [(authors’ note) takes their life].