Countermark

https://rpc.ashmus.ox.ac.uk/countermark/90 
GIC 818
denominational mark Ϛ
oval 
7 x 5 mm 
Probably a distinct group. It might belong in GIC 815, but the style of the numeral is different and Perge lies well outside the area from which the coins of 815 were drawn 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC IX, 1101 Show 1101 1 9