Green’s Dictionary of Slang

1. (orig. US, also finger, finger guy, finger merchant) a traitor, an informer; in criminal terms one who helps with a robbery ‘from the inside’.

1929		Hostetter & Beesley It’s a Racket! 224: finger man—Spy sent to meet, talk with, study the habits of, and observe the surroundings of someone.
1931		D. Runyon ‘The Snatching of Bookie Bob’ in Runyon on Broadway (1954) 119: The finger guy must know the party he fingers has plenty of ready scratch.
1938		J.E. Hoover Persons in Hiding 174: Robbers had deemed it necessay to hire a ‘finger man’.
1947		L.J. Valentine Night Stick 208: Rose, an ex-convict, frequented restaurants and tipped off his confederates of the appearance of wealthy women. Not only that, Rose followed these bejeweled women home, learning their addresses. We call such a man the ‘finger man’.
1952		(con. 1920s) ‘Harry Grey’ Hoods (1953) 53: The finger was an old and dependable connection.
1952		Lait & Mortimer USA Confidential 16: Burglars cannot operate without ‘fingermen’ who stake them out and fences who dispose of the loot–jewels, furs or hot money.
1961		J. Sparks Burglar to the Nobility 126: I never knew of a tip-off yet where there was as much money as the finger-man said their should be.
1967		(con. 1920s) J. Thompson South of Heaven (1994) 206: What had been Four Trey’s motive in acting as fingerman for the gang?
1973		E. Bunker No Beast So Fierce 44: And after three get heisted they’ll figure out who’s the finger man and string him up by his nuts.
1984		J. Ellroy Blood on the Moon 221: ‘I employed Lawrence Craigie as my vice finger man [...] He is a good snitch’.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 281: A cop finger man told them how the block search was breaking down.
2004		(con. 1982) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 270: A couple of the robbery team, who didn’t fancy spending the next decade in Parkhurst on the evidence of this disgruntled finger-merchant.
2012		T. Piccirilli Last Kind Words 264: ‘Hell of a card player. Hell of a finger man’.

2. a safebreaker.

1936

K. Mackenzie Living Rough 121: That’s a finger-man (a safe-blower), he opens cans.

3. an assassin.

1953

W. Hopson ‘The Ice Man Came’ in Thrilling Detective Winter 🌐 So you’re the finger man for that Eastern mob who found Joe. But you didn’t knock him off until you’d found the loot.

4. one who directs clients to a prostitute, casino, etc.

1953

‘John Eagle’ Hoodlums (2021) 71: A place where the finger man works in a downtown joint can’t be too dangerous.