This particular coin - a follis - was struck in early 312 AD in Nicomedia

Obverse: IMP C GAL VAL MAXIMINVS PF AVG, laureate head right

Reverse: GENIO A-VGVSTI, Genius standing left, modius on head, naked, except for chlamys over left shoulder (falls low), holding patera from which liquid flows, and cornucopiae. Right field: Γ. Mintmark SMN.

SMN stands for 'Sacra Moneta Nicomedia' - the mint in the city of Nicomedia where this coin was struck.

The Γ in the right field is a gamma - the third letter in the Greek alphabet - and signifies that this coin was struck in the 3rd workshop in the Nicomedia mint.

I like this coin a lot because it's in such excellent shape :) Pretty much as struck, except for the silvering which is gone.