Countermark

https://rpc.ashmus.ox.ac.uk/countermark/925 
GIC 811 ii
denominational mark Ϛ
circular 
7 mm 
probably applied at Ephesus, but not certain 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC VIII, — (number not assigned), type ID 20464 Show 1209 5 8
RPC VIII, — (number not assigned), type ID 20464 Show 1209 8 8
RPC X, — (number not assigned), type ID 60917 Show 1770 4 10
RPC V.2, — (number not assigned), type ID 705 Show 3574 3 5.2