https://rpc.ashmus.ox.ac.uk/countermark/739 

GIC 613

monogram ΔΙΟ

incuse square 

5 x 5 mm 

Corcyra (Epirus)

Διὸ(ς). Zeus Kasios - applied to (very) worn coins. It seems Corcyra produced no coins of their own from late Hellenistic until Antonine times and GIC 532, GIC 544 and GIC 613 likely sanctioned continued circulation