Dog tags is an informal name for the identification tags worn by military personnel.
The tag is used for the identification of dead and wounded and essential basic medical information for the treatment of the latter, such as blood type.
The dog tags are worn by military members of the SGC such as General Jonathan J. O'Neill, Samantha Carter, Colonels Cameron Mitchell and John Sheppard.
SG-1 found the Dog tags of Lt. Thomas Frakes after he had been burnt by Captain Jonas Hanson on the planet Avnil. (SG1: "The First Commandment")
Lt. Colonel John Sheppard finds the Dog tags of Major Evan Lorne on the burnt body of a Genii on the planet M1K-177. (SGA: "Coup D'etat")