Countermark

https://rpc.ashmus.ox.ac.uk/countermark/682 
GIC 553
ΝΙΚΟ
incuse 
variable 
often with GIC 782 (Δ) 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC IV, 4338 (temporary) Show 2633 7 4.1
Show 353
Show 445
RPC IV, 4337 (temporary) Show 2636 8 4.1