Green’s Dictionary of Slang

snake n.2

1. (US Und.) a railroad switchman.

[US]Wash. Post 10 Dec. 4/5: ‘Snakes’ are switchmen.
[US] in Randolph & Legman Ozark Folksongs and Folklore (1992) I 254: A snake run out to throw the switch, / The train ran over the son-of-a-bitch.
[Can](con. 1920s) O.D. Brooks Legs 21: And before you ask me what a snake is, it’s a switchman.

2. (Aus.) a non-commissioned officer.

[Aus](con. 1941) E. Lambert Twenty Thousand Thieves 176: Baxter reckons the officers and snakes are pinching our beer.

3. (US) a police officer.

[US]J.G. Rothenberg ‘Peanuts! The Pickle Dealers’ in AS XVI:3 Oct. 188: Tin badge, Flatty, Snake, Black and Blue, My Hero, Fagin. A policeman, used disparagingly.

4. a non union employment agency.

[US]M. Cherry On High Steel 199: I got a friend runs a little snake outfit; we’ll give him a call when the job’s done.