Countermark

https://rpc.ashmus.ox.ac.uk/countermark/841 
GIC 720
ΙΔ, or ΙΛ, or <Ι
Sometimes on reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 4445 Show 4445 1 1
RPC I, 4446 Show 4446 4 1
RPC I, 4446 Show 4446 2 1