Many Potsdam muskets that saw service in the civil war have a state surcharge, or an inspector's cartouche such as a flaming bomb on the bottom of the barrel. I've seen Potsdams with Ohio state surcharges on the stock , and the Safety Committee of Philadelphia on them. I would be very cautious of Southern surcharges on a Potsdam, just too many fakes. The northern surcharged Potsdam's are readily available and affordable compared to other original muskets.
Best Wishes:
Greg Edington