Sniffs are "highly developed psychometric" psychics who have the ability to observe past and present events of a specific person through extra-sensory perception by touching and smelling an object the target has recently touched. They can use their ability to monitor someone's movements and track them.
Their powers are activated using both their hands and nose, "sniffing" an object. Their sensitive touch means they usually wear gloves and only take them off if they want to use their abilities with greater accuracy.
The only effective method to prevent being tracked by a sniff is by using a Shadow.