Joe Enders: Stay on my ass.
Ben Yahzee: His name was Joe Enders, from south Philadelphia. He was a fierce warrior, a good marine. If you ever tell a story about him George... Say he was my friend.
Joe Enders: You think too much.
Private Chick: First time I've ever been accused of that.
Ben Yahzee: Sergeant, I'm telling you I won't freeze up again.
Joe Enders: Because your buddy smeared ash on your forehead?
Ben Yahzee: That's right, because my buddy smeared ash on my forehead.
Sargeant Ryan 'Ox' Anderson: How! Just kidding.
Answer: Marines (and other service members) wore their dog tags on the issued chains, or cords, string or other materials. This might have been for personal preference, available materials at issue, or replacement for breakages. So the costume designers probably copied this.