Countermark

https://rpc.ashmus.ox.ac.uk/countermark/265 
GIC 138
male head r.
square or slightly rectangular (one possibly circular) 
c5 mm square 
on coins of Claudius 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 4746 Show 4746 15 1
RPC I, 4746 Show 4746 13 1
RPC I, 4746 Show 4746 12 1
RPC I, 4746 Show 4746 1 1
RPC I, 4746 Show 4746 17 1
RPC I, 4746 Show 4746 16 1