Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1383 
GIC
REG (rectangular)
rectangular 
REG also appears on an incuse punch 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 675 Show 675 54 1
RPC I, 675 Show 675 47 1
RPC I, 675 Show 675 49 1
RPC I, 675 Show 675 50 1