Green’s Dictionary of Slang

croaker n.2

[? play on cripple n.1 ]

a silver sixpence.

[UK]B.M. Carew Gypsey of the Glen I iii: Be charitable, and put your fangs into your bungs, and throw us a croaker – All of us poor cripples.
[UK]Farmer & Henley Sl. and Its Analogues.