tags

"Dog tag" is an informal but common term for a specific type of identification tag worn by military personnel. The tags' primary use is for the identification of casualties; as such, they have information about the personnel written on them, and convey essential basic medical information such as their blood type and history of inoculations. They often indicate religious preference as well.
Dog tags are usually fabricated from a corrosion-resistant metal. They commonly contain two copies of the information, either in the form of a single tag that can be broken in half, or as two identical tags on the same chain. This purposeful duplication allows one tag, or half-tag, to be collected from a personnel's dead body for notification, while the duplicate remains with the corpse if the conditions of battle prevent it from being immediately recovered. The term arose and became popular because of the tags' resemblance to animal registration tags.

View More On Wikipedia.org