Green’s Dictionary of Slang

(US) the proceeds of a crime, a haul.

1928		J. Wilstach in Flynn’s Weekly 4 Feb. n.p.: ‘How much do you figure the first nick?’ ‘Oh, about ten grand’ [DU].
1935		(ref. to 1910) D. Maurer ‘Lingo of the Good People’ AS X:1 18/2: nick. a successful job.
1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 145/1: Nick, n. [...] 2. (Heard rarely but over widely scattered areas) A successful criminal coup; the proceeds of a crime; anything borrowed or begged; the act of obtaining anything by begging or borrowing.