Green’s Dictionary of Slang

1. (US) a police car that patrols the streets.

1934		R. Chandler ‘Finger Man’ in Pearls Are a Nuisance (1964) 89: ‘Snap it up,’ he said. ‘But that don’t mean trying to sideswipe a prowl car, if you lamp one.’.
1935		A.J. Pollock Und. Speaks n.p.: Prowl heap, a police radio car.
1946		J. Evans Halo in Blood (1988) 18: The prowl heap pulled in behind me.
1949		W.R. Burnett Asphalt Jungle in Four Novels (1984) 127: Prowl cars by the dozens, and harness bulls working in pairs. [Ibid.] 225: The way the prowls were going last night, every station in town must be full.
1952		W.R. Burnett Little Men, Big World 124: A prowl might show up.
1957		Kerouac On The Road (1972) 66: He called the prowl car in town. They came and took him away.
1958		E. Aarons Gang Rumble (2021) 11: Lew McGee, who was Vallera’s partner in the prowlie.
1968		D. Ireland Chantic Bird 179: I thought they might have signalled a passing prowl car.
1973		G.V. Higgins Digger’s Game (1981) 141: The Newton Police [...] parked four prowl cars near Pavilion.
1978		S. King Stand (1990) 171: The county prowler car.
1983		T. Paulin ‘Descendancy’ in Liberty Tree 19: I’ve a second cousin / drives a prowl car / in downtown Vancouver.
1990		(con. early 1950s) J. Ellroy L.A. Confidential 11: Bud ran to his prowler, hit the two-way.
1999		E. Bunker Mr Blue 244: I bought it [i.e. a gun] from him. I think he got it out of a prowl.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 155: A prowl car drove by. The cops scoped the game.
2003		McGill Reed Dict. of N.Z. Sl.
2021		J. Ellroy Widespread Panic 284: The backseat of a beat-to-hell prowl car.

2. attrib. use of sense 1.

1938

R. Chandler ‘Red Wind’ in Red Wind (1946) 15: The prowl-car boys came in about eight minutes.