Green’s Dictionary of Slang

1. to kill someone by pushing them from a moving train.

1932		D. Hammett ‘Too Many Have Lived’ in Nightmare Town (2001) 313: What’s the circus and carnival slang for kicking a guy off a train while it’s going? Red-lighting. Sure, that’s it.
1949		Monteleone Criminal Sl. (rev. edn) 191: red light [...] to kill.
1953		F. Brown Madball (2019) 122: The time on the freight train when he’d red-lighted the loud-mouthed shade.
1962		Ragen & Finston World’s Toughest Prison 815: red light – To do away with.

2. to ambush and rob couples in parked cars by flashing a red light and pretending to be a police officer.

1954

(con. 1948) C. Chessman Cell 2455 274: For weeks a ‘red light’ bandit had been terrorizing the inhabitants of Los Angeles County.

3. (Aus. prison) to expose onself.

1988

‘Siriusly’ Speaking in Just Us (H.M. Prison, Beechworth, Vic.) Dec. 27/1: red-lightv.Exhibiting onself indiscreetly (he was drunk, and red-lighting near the screws).