dog tag

noun
1.
a small disk or strip attached to a dog's harness or collar stating owner, home, etc.
2.
identification tag.
3.
Informal.
  1. any tag for a suitcase, camera, or other personal possession with the owner's name or address.
  2. a tag or card with a person's name or affiliation, worn at conventions, large meetings, etc.
Origin
1915-20
British Dictionary definitions for dog tags

dog tag

noun
1.
(US, slang) a military personal-identification disc
Slang definitions & phrases for dog tags

dog tags

noun phrase

Identification tags, esp metal tags worn around the neck by members of the armed forces: Vets, if you still have your dog tags

[WWI armed forces; each soldier had two : one to be taken from his body if he died, the other to be left with it]