I've been researching a coin of Constantine I from Thessalonica, and I came across an interesting sentence in RIC concerning the transition from the [dot]SM[dot]TS[dot] mint mark, with the officina letter in the field, to the [dot]TS[dot]A-E[dot] mark: "Absence of the hitherto prevailing SM indicates the withdrawal of Licinius' imperial treasury form Thessalonica in the face of Maxentius; threatened invasion of Europe." Really? I've long wondered why some mints include SM in their mint marks while other don't. Does the SM indicate the physical presence of some sort of imperial treasury in the city at the time of the coin's issuance?
