Countermark

https://rpc.ashmus.ox.ac.uk/countermark/451 
GIC 331
eagle l., head r., wings half open
circular 
5 mm 
The cmk may be related to the type of Zeus used by the city. They were applied with reference to the denominations: 331 to the smaller coins with Dionysus on the reverse and 444 to the larger coins of Domitian and Domitia with Zeus on the reverse. 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC II, 1263 Show 1263 8 2
RPC II, 1263 Show 1263 10 2
RPC II, 1263 Show 1263 14 2
RPC II, 1263 Show 1263 17 2
RPC II, 1263 Show 1263 18 2