Strange Orb

I was rooting around in my vegetable patch with the intention of digging up some nice new potatoes for lunch when <clang> my fork hit something.? I dug into the dirt and pulled out this object. It was covered in mud which I have since washed off, but does anyone know what it is ? Feels and looks like brass but is warm to the touch. It has lots of symbols carved into it, anyone make any sense of it ?