Great rifle! I guessed it to be of Swiss origin too, simply because of the "au" in the signature. I have a heavy percussion schuetzen made in Highland, Illinois, by a Swiss born gunsmith named Dominick Wiget. It is signed in script: "D. Wiget au Highland Ill". I believe that Tom Rowe also did a book on European Schuetzen rifles, or was at least working on one. His book on American Percussion Schuetzen Rifles is superb! I have never seen better photos in a gun book.
I have a dozen or so percussion schuetzens, all American made (all Upper Mississippi Valley, actually). Hinged trigger guards with thumbscrews, for quick removal of the trigger assembly, are pretty much the rule, rather than the exception.