Countermark

https://rpc.ashmus.ox.ac.uk/countermark/736 
GIC 610
monogram ΒΤ or ANTO..?
square 
5 x 5 mm 
BT.. or ANTO..? 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC IV, 4738 (temporary) Show 4034 3 4.1
RPC IV, 4738 (temporary) Show 4034 1 4.1