Question

Why are dog tags called dog tags?

Answer 1

If you've ever gone through basic training in the army, you get
this right away. The soldiers ID Tags resemble actual dog tags and
you get treated worse than a dog until you've earned the right to
be called a soldier, paratrooper, marine, sailor, or airman.

Answer 2

"Dog tags" is the informal term for the identification tags worn by military personnel, because of their resemblance to actual Dog tags.

Dog tags (called "identity discs" in the UK) are usually fabricated from a corrosion-resistant metal although they have been made from whatever was available.

Answer 3

Among the first instances of the identification tags being called dog tags comes from the Prussian Army in 1870. It comes from the term hundemarken which was similar to what each dog in the then Prussian capital of Berlin required. The American adaptation of the name dates to just before WWII.