Green’s Dictionary of Slang

(US Und.) a dollar.

1903		Our Naval Apprentice Nov. 129: He has plenty of ‘Dobies,’ he’s out for sport [HDAS].
1907		C. M’Govern By Bolo and Krag 18: It was bought [...] by a bunch of grafting town officials of Talisayan itself out of dhobes squeezed from the local tauaos [i.e. common people].
1917		Van Loan ‘The Last Chance’ in Old Man Curry 126: He bet the wad – two great big iron dobey dollars – all at once, mind you!
1933		Ersine Und. and Prison Sl.