Green’s Dictionary of Slang

holler copper v.

to inform.

1927		D. Runyon ‘A Chilly Looking Blond’ in Brookhouser These Were Our Years (1959) 210: Mrs. Snyder and Gray have been ‘hollering copper’ on each other.
1931		D. Runyon ‘Dream Street Rose’ in Runyon on Broadway (1954) 45: He is not going to holler copper about it.
1940		Black Mask Mar. XXII 10: Not my contract. I holler police. I squawk to Jim Farley.
1944		D. Runyon Runyon à la Carte 175: I will never forgive myself if I am compelled to holler copper on anybody whatsoever.
1953		K. Tennant Joyful Condemned 21: Don’t let’s have any blues [...] You know how the brush are? Screaming and yelling copper at the least little thing.
1955		B. Schulberg On the Waterfront (1964) 246: You mean holler cop? Are you kiddin?
1959		J. Thompson Getaway in Four Novels (1983) 58: You holler copper and you and Frannie get your clocks fixed.
1965		F.J. Hardy Yarns of Billy Borker 61: Some mug is bound to squeal coppers sooner or later.
1968		(con. c.1900) J. Thompson King Blood (1989) 25: She tipped the ‘fool’ she had roped, and the fool hollered copper.
1971		T. Thackrey Thief 191: Give the girl a silver dollar; you didn’t holler copper.
1972		(con. 1930s) N. Algren ‘The Last Carousel’ in Texas Stories (1995) 140: When hit with the swag when the hooks were out, they could take a drop without hollering cop.
1988		D. Woodrell Muscle for the Wing 188: I didn’t holler cop.
1991		(con. 1920s) O.D. Brooks Legs 179: We hightailed it too, in case he hollered copper.