Originally metal disks embossed with personal information that could be left with a body on the field of battle for identification. Eventually it evolved into a rounded rectangle with a small indentation on one side so that it could be set on the teeth of a deceased soldier and kicked into the head so that the enemy could not strip the dead soldier of his identity (this info confirmed with HQMC Casualty Branch). Current versions do not have the notch. (see also Toe Chain.)