Green’s Dictionary of Slang

(US Und.) money, usu. stolen.

1904		Number 1500 Life In Sing Sing 261: As I had plenty of the darb I blew away and beat it back to Chic, and framed in with a couple of guns who were working east on the rattlers.
1919		A. Baer in Atlanta Constitution 23 Nov. A2/4: Back to the office, where Citronella breaks out a pair of dice. [...] Simpie cops all the Darb.
1928		M.C. Sharpe Chicago May (1929) 31: ‘Say, kid,’ says he, ‘I’ve got the darb (stolen money).’.
1949		Monteleone Criminal Sl. (rev. edn).