Countermark

https://rpc.ashmus.ox.ac.uk/countermark/812 
GIC 691
Χ?
On reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC II, 1237 Show 1237 1 2
RPC II, 1237 Show 1237 2 2
RPC I, 2856 Show 2856 23 1