Countermark

https://rpc.ashmus.ox.ac.uk/countermark/797 
GIC 673
Μ or Σ
rectangular 
6 x 3 mm 
Ionopolis Abonoteichos (Paphlagonia)
probably to be read as M, because if it was a sigma one would expect the lunate form at this date 
List of countermarks View on a map

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC IV, 5361 (temporary) Show 4371 2 4.1