Countermark

https://rpc.ashmus.ox.ac.uk/countermark/893 
GIC 760
denominational mark Β
circular 
5 mm 
GIC lists this cmk for coins of Cyme, Temnus, Clazomenae and Phocaea. Probably linked with GIC 791 - denominational mark Δ 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC VIII, — (number not assigned), type ID 20330 Show 1058 22 8
RPC X, — (number not assigned), type ID 59777 Show 1590 10 10
RPC VIII, — (number not assigned), type ID 59799 Show 1084 15 8
RPC VI, 30792 (temporary) Show 3838 13 6
RPC X, — (number not assigned), type ID 59777 Show 1590 25 10