Quiet Aura

The character or object with a quiet aura will not detect as their specific creature type. Very, very few creatures are able to masquerade the fundamental type of being that they are. It cannot be discerned with Aura Sight.

D20 Quiet Aura Mechanics

Foils the use of Detect Evil/Good, unless they are in direct service to a patron of that type, or are using special abilities that channel that connection.

Incarna Core Quiet Aura Mechanics

Having trouble thinking how this might play out after reading this? Check out the Players Roleplaying Guidance or ask the Game Master how it is best expressed in the setting.