Countermark

https://rpc.ashmus.ox.ac.uk/countermark/803 
GIC 680
Ν
circular 
5 mm 
host coin was unidentified in GIC with note "perhaps a Peloponnesian cmk"; on reverese 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 1740 Show 1740 5 1
RPC I, 1740 Show 1740 10 1