Green’s Dictionary of Slang

(US) a police patrol wagon.

1886		On and Off Duty 52: Two officers accompany the ‘hoodlum wagon’ — one in charge of the horses, a second to take charge of the prisoner.
1887		Eve. Bulletin (Maysville, KY) 29 Nov. 2/2: The hoodlum wagon is summoned, and the limp form is carried to the calaboose and hustled into a cell.
1895		Wichita Daily Eagle (Kansas) 20 Aug. 5/3: As he has plenty drivers, he can operate the hoodlum wagon very handily.
1902		Mexico Missouri Message (Audrain Co., MO) 2 Oct. 1/2: The hoodlum wagon [...] with a couple of big policemen.
1908		H. Green Maison De Shine 237: We’ll git out by mornin’, sure. Farewell all, an’ say how Maggie de Shine went to the hoodle-hoodle waggin like Mary Queen o’ Scots to her finish!
1917		Alliance Herald (Box butte Co., Neb) 5 Apr. 7/2: Silas Hyndshaw [...] an expert driver of the ‘hoodlum wagon’.
1922		Durant Wkly News (Choctaw Nation, OK) 17 Feb. n.p.: The Legion cops expect to catch all the ex-service men [...] load them into the hoodlum wagon, carry them before a judge and have a trial.
1943		W. Guthrie Bound for Glory (1969) 357: A big long black hoodlum wagon drove up and fifteen or twenty cops fell out.
1965–7		in DARE.
2001		F. Grace Carry A. Nation: Retelling the Life (2004) 241: The officers threw the women into a ‘hoodlum wagon,’ carting them down to the station ‘amidst yells and execrations.’.