Green’s Dictionary of Slang

(US Und.) a piece of paper that facilitates begging (cf. screeve n.).

1903		N.-Y. Trib. 10 May B 1: Most of these are armed with a supply of ‘duckets,’ or ‘dockets’ – that is, cards on which are printed in rambling doggerel an appeal for alms.
1907		N.Y. Times 27 Jan. Sun. Mag. 4: Then there are [...] the bogus labor men and sailors, the ‘old soldiers’ with missing arms bandaged to their bodies under their shirts, and the old, feeble, or diseased with printed appeals, or ‘dockets’.