Countermark

https://rpc.ashmus.ox.ac.uk/countermark/304 
GIC 177
head r.?
GIC references NZ (Numismatishe Zeitschrift, Vienna) Ancyra (Phrygia) Civic 3rd century. Johnson Sardis 333: not verified 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber