Green’s Dictionary of Slang

(US) female and male toilets respectively; collectively, a generic term for the lavatory.

1935		J. Conroy World to Win 275: One guy I know follows his customers into the neat little room marked ‘Papa’ or ‘Jiggs’ just across from the one marked ‘Mama’ or ‘Maggie’ with a roll of tissue in his mitt.
1950		WELS [DARE].
1968		in DARE.