Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1569 
GIC
X, in square, in circular punch
circular 
4.5 mm 
on a coin of Lampsacus; no certainty applied at Lampsacus 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 2278 Show 2278 7 1