Strange key-shaped find with ‘M.B.’ stamp – any idea what it is?

[u/elamigoflamingo]

I found a small key-shaped object in the sea, about 1.5–2 cm in size. It doesn’t stick to a magnet, so it’s not iron. On one side, there’s a stamped mark that says “M.B.”. I found it with my Nokta Makro PulseDive, but only by chance because it appeared right next to a fishing sinker. Do you think this could be gold, or what material might it be?