This is not a new thing. We have a large outlet mall across the street (which is nearly dead now). We have done a lot of work at these stores under contract to a large marketing/sign company which does all the stores for the company. Stores like Coach, Nike, Adidas, Polo, Reebok, and so on. Since the work usually was inside the store putting up marketing materials and display signs and often during business hours, there were always requirements for dress. They did not want you wearing clothing that advertised your own business. Typically they wanted plain solid color shirt, often a collared shirt. They did not allow any competitor logo clothing or shoes. So for the running shoe companies I either had to wear their brand shoe or something unadorned like brown boots. And since you are working inside their business as their contract employee by proxy, it is perfectly reasonable to require you to act appropriately.
The funny part is when customers come to you asking about products or where to find something.
