Countermark

https://rpc.ashmus.ox.ac.uk/countermark/561 
GIC 440
star of 6 rays
circular incuse 
4 mm 
On obverse and reverse. GIC had host as being from Lampsacus, not Imbros 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 1738 Show 1738 1 1
RPC I, 1738 Show 1738 1 1
RPC I, 1738 Show 1738 2 1
RPC I, 1738 Show 1738 2 1
RPC I, 1738 Show 1738 3 1
RPC I, 1738 Show 1738 3 1