Green’s Dictionary of Slang

1. a silver sixpence.

1830		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.
1890–1904		Farmer & Henley Sl. and Its Analogues.

2. (UK und.) a fourpence coin.

1935

Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks n.p.: Croaker: Fourpence.