dog tag 
noun
1A metal tag attached to a dog’s collar, typically giving its name and owner’s address.But last month, Beryl received a phone call from a woman in Southport who said she had found Toby: he was still wearing his dog tag and collar....
- There was a glint of silver in her collar; a dog tag.
- Each copy also has a dog tag and doggie-snack (hence the name of the book) attached to the cover, to lure your lost pet home.
1.1North American informal A soldier’s metal identity tag.They have developed an identity medal that is fashioned after a military dog tag....
- An American businessman who had visited the regional military museum here in Dandong reported that he had seen a metal identification tag or dog tag.
- The government recently contracted with four private companies to reinvent the dog tag, which has changed little since the armed forces made wearing them mandatory in 1913.