Countermark

https://rpc.ashmus.ox.ac.uk/countermark/926 
GIC 811 iii
denominational mark Ϛ
circular 
6 mm 
probably applied at Ephesus, but not certain 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC X, — (number not assigned), type ID 61113 Show 1796 2 10
RPC V.2, — (number not assigned), type ID 146 Show 2643 4 5.2