Countermark

https://rpc.ashmus.ox.ac.uk/countermark/598 
GIC 471
thunderbolt
oval 
7 x 5.5 mm 
There was a famous temple of Zeus at Olba, and the thunderbolt was used as a type on coins 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC IV, 5831 (temporary) Show 1050 2 4.3
RPC IV, 6158 (temporary) Show 1045 3 4.3
RPC IV, 5831 (temporary) Show 1050 9 4.3