You can see auras through opaque objects, within certain limits. The SRD doesn't list flesh as being opaque to the spell, and if we took "wood/earth" as the closest material, you'd need a wall several feet thick. Most people aren't that big. So yes, a mage should be able to see an aura.
I'd imagine that it would look really strange, though. Most mages would probably assume the person was wearing an amulet under clothing, and then get confused when no amulet was found. Bonus points if the person actually is wearing an amulet, but then the amulet is removed and the aura is still (roughly) where the amulet was.