Countermark

https://rpc.ashmus.ox.ac.uk/countermark/966 
GIC 850
ΚΚ (on silver coins)
as 850i and 850ii 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 3637 Show 3637 1 1
RPC I, 3637 Show 3637 3 1
RPC I, 3637 Show 3637 4 1
RPC I, 3638 Show 3638 1 1
RPC I, 3638 Show 3638 2 1