Countermark

https://rpc.ashmus.ox.ac.uk/countermark/602 
GIC 475
thunderbolt
rectangular 
5.5–6 x 3.5 mm 
Possibly applied (with GIC 343) by XII Fulminata in the area of Neapolis in perhaps AD 115-117. Another explanation was that the eagle and thunderbolt referred to the cult of Zeus Hypsistos. It is difficult to date the cmks as late as the founding of the temple of Zeus under Hadrian. 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC II, 2218 Show 2218 8 2
RPC II, 2218 Show 2218 16 2
RPC II, 2218 Show 2218 17 2
Show 257
Show 248