Countermark

https://rpc.ashmus.ox.ac.uk/countermark/790 
GIC 662
Α?
circular 
6 mm 
as diameters of coins go from 23 to 31 mm, and weights from 6.72 to 18.23g, unlikely to be a denominational mark 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC V.3, — (number not assigned), type ID 74915 Show 690 1 5.3
RPC VI, 6070 (temporary) Show 5806 5 6
RPC VI, 6031 (temporary) Show 5757 4 6
RPC VI, 6059 (temporary) Show 5789 1 6
RPC VI, 6014 (temporary) Show 5742 1 6
RPC V.3, — (number not assigned), type ID 74905 Show 680 3 5.3
RPC VI, 6037 (temporary) Show 5776 6 6
RPC VI, 6051 (temporary) Show 5787 3 6