Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1425 
GIC
uncertain design (on silver drachm)
shaped 
c. 4 mm tall x 2 mm wide 
on a coin of Nero from Caesarea (Cappadocia) 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 3641 Show 3641 3 1