Green’s Dictionary of Slang

(US) a member of Pinkerton’s Detective Agency; thus the Pinks, the Agency as a whole.

[1875		M.D. Landon Eli Perkins 111: Half a dozen of Pinkerton’s men had ‘bit the dust’ hunting him down].
[1884		G.W. Peck Peck’s Boss Book 72: I am no Pinkerton].
1894		J. London Tramp Diary in Jack London On the Road (1979) 53: He gave the P’s a good talking to.
1904		Number 1500 Life In Sing Sing 6: I’m one of the Pinks! [Ibid.] 263: Pink had me framed and it was like finding rags to the pusher.
1908		Scribner’s Mag. XLIII 714/1: ‘I think he’s a Pink!’ ‘What nonsense,’ exclaimed Gaylor in alarm. ‘No detective would force his way into this house.’.
1915		G. Bronson-Howard God’s Man 114: The ‘Pink’ was Pink because he took devilish pleasure in causing Pinkerton race-track detectives to ‘look more than usually silly’ [...] by abstracting their watches on all possible occasions.
1931		Irwin Amer. Tramp and Und. Sl. 245: Let us not look too harshly upon the ‘Pinks!’.
1940		O. Ameringer If You Don’t Weaken 207: Why didn’t I warn you about that son of a bitch before! He’s a Pink (Pinkerton).
1949		N. Algren Man with the Golden Arm 236: The punk must be practicing to be a Pinkie again.
1949		Monteleone Criminal Sl. (rev. edn) 177: pink [...] pinkie [...] pink eye A Pinkerton detective.
1961		J. Scarne Complete Guide to Gambling 688: Pink – a racetrack detective.
1982		M. Braun Judas Tree (1983) 110: Maybe that’s why the Pinks lose so many men.
1992		R.C. Cruz Straight Outta Compton 29: Brothers and sisters cursed the cops and called them whips and pinks.