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 1093 2 4.3
RPC IV, 6158 (temporary) Show 1088 3 4.3
RPC IV, 5831 (temporary) Show 1093 9 4.3
RPC V.3, — (number not assigned), type ID 77528 Show 2508 4 5.3
RPC V.3, — (number not assigned), type ID 79557 Show 2511 3 5.3