Countermark

https://rpc.ashmus.ox.ac.uk/countermark/171 
GIC 50
two facing bearded busts (M. Aurelius and L. Verus?); on reverse
rectangular 
on coin of Ptolemais, but might not have been applied there? 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC III, 3911 Show 3911 5 3