Green’s Dictionary of Slang

(US) a female prostitute’s female client.

a.1963		‘The Fall’ in D. Wepman et al. Life (1976) 81: No Jean or John that whore couldn’t con, / ’Cause that trick was never born.
1972		B. Rodgers Queens’ Vernacular 117: Jane 1. lesbian client of a streetwalker.
2003		W. Mosley Six Easy Pieces 140: Mona was like heaven on earth and she never left a John, or Jane, unsatisfied.