Green’s Dictionary of Slang

sarah soo n.

a Jew.

1959		J. Gosling Ghost Squad 24: Thieves’ argot, spoken properly, is a foreign language which needs to be learned [...] Among the words and phrases derived from rhyming slang are: [...] Sarah Soo, Four-by-two or Kangar (Kangaroo) means a Jew.
1984		Partridge DSUE (8th edn) 1012/1: since ca. 1925.