Countermark

https://rpc.ashmus.ox.ac.uk/countermark/757 
GIC 634
monogram ΡΚΑ? on reverse
circular 
3 mm 
in circular punch c.3 mm. on reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 2961 Show 2961 1 1
RPC I, 2963 Show 2963 2 1
RPC I, 2965 Show 2965 1 1
RPC I, 2959 Show 2959 1 1
RPC I, 3147 Show 3147 21 1