By Erin Geiger Smith NEW YORK (Reuters) – Design companies tending to the details of fashion shows have more to think about than skirt lengths and handbag clasps – they must decide whether to seek U.S. patent protection for their looks. Diane von Furstenberg, famous for her wrap dresses, has a design patent on a chain mail-style bag. The popular French line Celine has one on the envelope-style handbag sported by countless fashion experts at New York Fashion Week. This summer alone, brands including Alexander Wang, Balenciaga and Tod’s all were granted design patents by the U.S. …