I have to disagree with you. This picture is the marking in question on my Potsdam. I could understand your point if it said "A. Wurfflein, Philadelphia." However it's obviously two seperate dies. Also Wurfflein is known to have had contracts with the City of Philadelphia to supply arms and ammunition and repair/update older arms. Finally, according to "Firearms From Europe" by Whisker, Yantz and Noe:
"The City of Philadelphia acquired an unknown number [of Potsdams] through its resident arms authority and procurer, Andrew Wurfflein, and these were marked on the barrels with the city's cartouche."
P.S.: If the picture didn't post, the URL is: