Countermark

https://rpc.ashmus.ox.ac.uk/countermark/753 
GIC 630
monogram ΠΡΟΥ
Prusias. On reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC II, 687 Show 687 7 2
RPC II, 687 Show 687 6 2
RPC II, 687 Show 687 9 2
Show 61
Show 94
Show 57