How to hang a silver tray on the wall?

Without knowing the size of the tray I would think that a plate hanger could work. You could also try using fishing line.

Glue a fabric backed hanger to the back of the tray. Then hang like a picture.

Get a large plate hanger that's what I used it works great

Plate hangers - sold everywhere, you don't have to buy on line, here is an example.

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Hi Jo! I highly recommend using Command picture hanging strips. I've used them for everything from mirrors, framed pictures, wreaths, and paintings. I prefer the large ones that are rated for 16 pounds.