I don't really find the prospect appealing. We don't have a plague hanging from our neck, or a brand on our foreheads, to tell our alignment, now do we? Reputation, as is, is a lot more logical. (Maybe implement a counterpart. If you're with the thieves' guild, for example, you increase your "reputation" in the underworld.) Besides, evil people don't always look evil. You, of all people, should know that. What with TNO being zombie-like and can still persuade people using those dark, murky, charismatic eyes of his - irrespective of his alignment.