Countermark

https://rpc.ashmus.ox.ac.uk/countermark/792 
GIC 665
Α
incuse 
5.5 mm tall 4 mm at base of A 
GIC had A?, but 2nd example clearly shows A; on reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC VI, 8852 (temporary) Show 8711 3 6
RPC VI, 8852 (temporary) Show 8711 2 6