Unknown object, possible ID tag of some sort?

[Pregeo]

Good day,

Found this object next to a former POW camp in northern Germany. It is known that at least French marines were kept prisoner over there.

Measures 30 mm in diameter.

Any information and suggestions are very welcome, I have no idea what it could be.

[BlackCat1982]

Not so much an identity tag but more likely an inspection tag for a piece of naval related equipment. It's a nice find, but currently a mystery as to what it came from.