Countermark

https://rpc.ashmus.ox.ac.uk/countermark/674 
GIC 545
Κ.Θ
rectangular 
4 x 3 mm 
Claduius, year 9 = AD 49 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 3657 Show 3657 3 1
RPC I, 3657 Show 3657 4 1
RPC I, 3657 Show 3657 5 1