Mappin & Webb is a very old manufacturer of silver items. It dates all the way back to 1775 and is still in business today. Your tray is silver plate. The term "Prince's Plate" was used from about 1890 to 1900 (can't be precise). The code w16062 would be a pattern number. The other symbols may nail the date down more specifically, but I can't find a code index to match it to. Luckily, as I said, Mappin & Webb is still in business. You can contact them through their website and simply ask them. I'm sure they have an archive that can help you further identify your tray.