Seal of some kind. Bag seal or seal for anything. If you can get the details on the symbols you may be able to attribute it to something. I have found then from simple bag number to military markings.
I was fortunate to detect Caribbean island. found lead items (pistol and musket balls) plus scrap lead, bronze ship spikes, and buttons. One british navy buttone from early 1800's. Best find was slave jewelry. Broken but the three links represented manilla, the bronze rings europeans used to buy slaves in Africa. In Africa, the chief with the most of these rings was rich. Slaves were bought with manilla, not gold or silver. This jewelry I found represented a high level slave. Most likely still worn after their freedon when slavery abloished in 1834.