Green’s Dictionary of Slang

(US) Jewish.

1937		(con. 1905–25) E.H. Sutherland Professional Thief (1956) 12: I [...] saw this Jew who was pointed out to me as one of their best mocky cannons.
1955		PADS xxiv. 90: Jewish organizations are referred to as mocky mobs or mocky jew mobs. ‘Mocky is not a Jew. It’s a Sixth Avenue Jew.’.
1992		R.G. Barrett White Shoes 117: Just don’t tell my mockey boyfriend.
1992		R.G. Barrett White Shoes 268: The rotten little mockey bastard.
2004		J. Ellroy ‘Jungletown Jihad’ in Destination: Morgue! (2004) 384: The Oscars. [...] The Sheeny Shangri-la, the Mockie Matterhorn, the Kike Kilimanjaro. More Jews than the Old Testament.