Green’s Dictionary of Slang

pigeon drop n.

also dropping the pigeon
[pigeon n.1 (2a)]

[mid-19C+] (US Und.) a confidence trick that involves dropping a wallet where a victim can find it or a scheme in which the con-man tells the victim that they have found a large sum of money and, if the victim will advance some money as a show of good faith, they can have a share in the ‘windfall’.

In compounds

pigeon dropper (n.)

[mid-19C+] (US Und.) a confidence trickster.

pigeon dropping (n.)

[mid-19C+] (US Und., also pigeon drop, pigeon game, dropping the pigeon) playing any form of confidence trick.