You have disturbing features that mark you as a demon, vampire, or other supernatural being. You can pass for a normal mortal to casual observers, but closer inspection reveals that you are not quite right. This might give away your secret to the trained eye.
Supernatural Features differ from Unnatural Features in that they aren’t usually obvious; they only become apparent under a specific set of circumstances. When they are noticed, though, they result in a reaction penalty. They also give those who know what to look for a bonus to any skill roll (against Hidden Lore, Occultism, etc.) made to identify your true nature.