Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1490 
GIC
GAL CA
rectangular 
c. 19 x 4 mm 
Martini 2.1425-6. Is variant from GIC 591 (GALBA) 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 1758 Show 1758 7 1
RPC I, 1960 Show 1960 4 1