Unless you're running up to people and stopping, dressing in a death robe, etc, it shouldn't matter. This age in the game appearances don't really give away a thief anymore. Mostly because people don't think thieves play much since insurance was added.
But to really hide yourself, stealth around people
I am almost always hidden/stealthed. I use shadow jump to get next to people most of the time and use it to jump away from them. So they never see me to begin with.