Originally Posted by moving0target

It's called a "gorget" and it was usually worn by their version of military police. It led to the MPs being slangily referred to as "chained dogs."

More abstract, a gorget started off as the piece of armor that covered the upper chest and lower neck where the breastplate, shoulder plates, and helmet meet. Later, it shrank in size to something more ornamental and was used to signify everything from rank to coat of arms to unit.