https://rpc.ashmus.ox.ac.uk/countermark/637 

GIC 510

ΑΔ

rectangular 

4 x 3 mm 

Uncertain (Uncertain)

Hadrian (1). BMC 591 as Corinth. GIC followed BMC as recording for Corinth when coin is actually from Pella. As Pella was a Latin colony, unlikely that Greek letters would have been used