This thing was found on the lawn in a residential garden about 4m from the side fence wall with a 2 story apartment building.

It is not attracted by a magnet -
Material ss316.
About 11mm thick on the widest part.
The 2 spoon shaped halves were welded together and the joints were machined to a rounded, smooth polished surface.
It is hollow inside but may have something inside.
It floats on water.
The weld is good with no leaks.
There is no attaching mechanism. and no clamping marks.
The only marking is a very slight pimple caused by something sharp from the inside.
My question is - Do you know of any machine or equipment that may use a thing like it.
If not - what do you think it is. I have a 2 suspicions but will rather wait for an answer.
The garden is south of Pretoria , South Africa.
Thanks for any help.