Wikipedia
Signaculum
A signaculum was a lead " dog tag" in a leather pouch carried by Roman soldiers around their neck. It seems to have had personal details (acting to identify a body the same way a modern dog tag does) with a seal or stamp to authenticate it.
Similar items for identifying civilian goods and equipment have been found as well. Signacula of this variety were not discs that were carried on one's person as with the Roman army equivalent, but are more like modern-day product labels, giving information on the item's manufacturer and affiliates.