Countermark

https://rpc.ashmus.ox.ac.uk/countermark/748 
GIC 625
ΝΚ monogram
circular 
Thessalonica likely but not certain. Nero Caesar? 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC I, 1554 Show 1554 91 1
RPC I, 1554 Show 1554 92 1
RPC I, 1554 Show 1554 93 1
RPC I, 1554 Show 1554 94 1
RPC I, 1554 Show 1554 96 1
RPC I, 2235 Show 2235 40 1
RPC I, 1554 Show 1554 99 1
RPC I, 1554 Show 1554 100 1