Countermark

https://rpc.ashmus.ox.ac.uk/countermark/284 
GIC 155
laureate head l.
circular 
9 mm 
Sometimes on reverse. They may have been applied at Neapolis (Samaria), but the provenances of GIC 408, with one example paired with GIC 155, give some reason to doubt Neapolis 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC II, 2218 Show 2218 16 2
Show 155
Show 138