Countermark

https://rpc.ashmus.ox.ac.uk/countermark/840 
GIC 719
ΙΛ°| or inverted (depending on the orientation)
rectangular 
6 x 3 mm 
It is tempting to interpret this as a legionary cmk LVI or XVI, but it is more probable that it is a local cmk. It is applied in the same way as GIC 511 (ΑΔΡ) and 529 (ΔΑΚ) and may be a garbled version of one of them. 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC III, 3812 Show 3812 27 3