A temporal tag was a 31st century technological device that allowed an object to be marked for retrieval from another time period.
In 2153, Daniels provided Captain Archer with temporal tags when he sent Archer and T'Pol to Earth, 2004, to stop a temporal incursion by the Xindi. After defeating the Xindi, they were able to use the tags to mark everything that didn't belong in that time for transportation back to 2153. (ENT: "Carpenter Street")