[sergior]

Coin has WiFi and a microphone and sends data to the nearest surveillance spot if it is in range.

[marcosdumay]

If they weren't metallic, it wouldn't be a bad idea to put some RFID in them, or even set some secret handshake to automatically detect false coins.

[cat199]

There is likely an embedded known hash/serial number/other identifier in the U/V signature for exactly this.