https://rpc.ashmus.ox.ac.uk/countermark/944 

GIC 826

denominational mark Η

circular 

7.5 mm 

Amastris (Paphlagonia)

since the Delepierre SNG France 7, no 142 had GIC 826 overstamped by GIC 43, it must have been applied before AD 244. Hence it was earlier than the H countermarks on nearby Heraclea and Tium. Since it is on a coin of Amastris and has been overstamped by another countermark at Amastris, the most economical explanation is that it was itself applied at Amastris.