Countermark

https://rpc.ashmus.ox.ac.uk/countermark/599 
GIC 472
thunderbolt
rectangular 
8 x 4 mm 
Sometimes on reverse. Almost certainly a countermark of XII Fulminata. Found on Antioch S C coins 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 4280 Show 4280 9 1
RPC I, 4277 Show 4277 10 1
RPC I, 3868 Show 3868 24 1
Show 372
RPC II, 2023 Show 2023 70 2
Show 171
RPC I, 3868 Show 3868 43 1