Green’s Dictionary of Slang

(US Und.) a professional beggar.

1918		‘A-No. 1’ Mother of the Hoboes 65: The plinger had judged correctly. The enraged travelers were the keepers of the public pound.
1928		J. Callahan Man’s Grim Justice 132: The well-dressed boys were the Johns and the plingers, the professional tramps who could go out on the drag and get most anything they wanted.
1935		A.J. Pollock Und. Speaks n.p.: Plinger, a beggar.
1940		D. Maurer Big Con 210: Giving money to a plinger is always good luck.
1950		Goldin et al. DAUL 161/1: Plinger. One who plings [i.e. begs].
1950		Asheville Citizen Times (NC) 20 Nov. 8/3: Choice mooching spots for [...] ‘plingies’ (professional panhandlers) and ‘dingies’ (plain bums).