Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1740 
GIC
uncertain, but possibly ΔΡ or Δ with line from r. side of triangle
circular 
6 mm 
on coins of c. 30 mm diameter. Probably a denominational mark? 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC V.2, — (number not assigned), type ID 942 Show 3661 4 5.2
RPC V.2, — (number not assigned), type ID 942 Show 3661 3 5.2
RPC V.2, — (number not assigned), type ID 239 Show 3656 3 5.2