The Smith & Wesson name on the front of the muzzle on the right side is the import markings. Before S&W it was Walther USA, and Carl Walther USA before that and so on.
All P99's are made in Germany. The only exception was that a few 40SW slides were made in the US by S&W. This was before the design change and these few 40SW P99's are easy to spot, as they do not have the Eagle over N proof make on the slide.
There is no difference in the pistol, just because of the S&W import marking on it. I have ones marked "Carl Walther USA LLC", "Walther USA", and "Smith & Wesson". All 100% German made.