If Parallels Desktop is in full-screen mode there is no way you can tell, by looking at a Mac or watching a person use it, whether Windows uses Parallels Desktop or is running native. You would have to either ask its user or press Alt-Enter (Option-Enter in Macspeak) to try to return Parallels Desktop to windowed mode and see if it does. "Wander through my local Starbucks and see" doesn't suggest that you did either of these.