An unusual Shipwreck Slab - Updated
This 1861-O Half was apparently recovered from the S.S. Republic. A typical label would mention the ship, date, mintmark.
Furthermore, NGC would designate the quality as either:
A, B, C or no letter with other qualifiers/ grades. I haven't seen one like this before:
Looks about MS61 or 62 with that subdued saltwater look.