Countermark

https://rpc.ashmus.ox.ac.uk/countermark/673 
GIC 544
ΚΑϹΙΟ
rectangular 
11 x 3 mm 
(Zeus) Kasios - applied to (very) worn coins. It seems Corcyra produced no coins of their own from late Hellenistic until Antonine time and GIC 532 and GIC 544 likely sanctioned continued circulation 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
Show 155
Show 156