According to this answer, wearing a toupee without a kippa on top may pose a problem of maris ayin.
My question is: Suppose the toupee-wearer has no distinctive Jewish features other than wearing a kippa. In this case then, nobody would know he was Jewish unless he is in an area where people know him. Suppose he's in an area where nobody knows him. Would it still be maris ayin? If so, why?