Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1641 
GIC
Γ in shaped punch
shaped 
5 mm long 3 mm for bar of the Γ 
 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
Show 142
RPC IV, 6179 (temporary) Show 1315 8 4.3
Show 193