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
RPC IV, 6179 (temporary) Show 1343 8 4.3
Show 197
RPC II, 1784 Show 1784 7 2
RPC IV, 17282 (temporary) Show 1338 3 4.3