Countermark

https://rpc.ashmus.ox.ac.uk/countermark/1427 
Martini, Pangerl 103
AM (Latin) or ΑΜ (Greek)
rectangular 
7 x 3 mm 
applied in Syria to a Tiberian dupondius 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 3868 Show 3868 16 1