Countermark

https://rpc.ashmus.ox.ac.uk/countermark/900 
GIC 770
denominational mark Β (sometimes on reverse)
circular 
5 mm 
applied with GIC 125, sometimes on same side, other times on different sides 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC III, 4099 Show 4099 55 3
RPC III, 4099 Show 4099 54 3
RPC III, 4099 Show 4099 56 3
Show 88
Show 212
Show 122