https://rpc.ashmus.ox.ac.uk/countermark/1166 

GIC —

Cnossian monogram including AS?

circular 

6.5 mm 

Cnossus (Crete)

RPC I, p. 223: This countermark was applied without consideration of weight, perhaps after 27 BC, to allow these coins to circulate throughout the province. It might be resolved as the word CRETA (NC, I949, p. 43) or hide the name of a Roman official (Price). The first solution seems unlikely, as the countermark appears to include the Latin letter S, and possibly also an A. Could it be a mark of value, an as?