Green’s Dictionary of Slang

(US black) 25 cents, a quarter.

1940		D. Burley N.Y. Amsterdam News 19 Oct. 20: quarter is a ‘double-ruff’.
1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 259: ruff (n.): quarter, twenty-five cents.
1945		C. Himes If He Hollers 127: I run into this gray boy [...] and we got to jawing ’bout a ruff we found on the street.