Green’s Dictionary of Slang

a term of endearment.

1914		F. Dumont Darkey Dialect Discourses 15: If she whacks you on the right cheek, turn de left one to her and say soak me again, petty, and maybe she will.
1915		G. Bronson-Howard God’s Man 370: Mr. Roy Schmucke, from having been ‘Petty’ to so many female admirers, was ‘Petty Schmucke’ even to the manly loungers who hailed him jovially on his entrance to each bar.