Hi Pat,
The site is primarily about silver producers, not silverplate makers, but many American companies made both products. Some of these used different trademarks to differentiate between silverplate and sterling, but others did not. So often, the same trademark can be seen on both sterling and silverplate. If the piece is American and sterling, you can rely on the fact that it will be clearly stamped "STERLING" or "925" or "925/1000". If the piece is silverplate you may just have the company trademark, as on your tray, but possibly it may have the addition of EPNS or EPC to let you know the material used. You can look onsite in the
Silver Glossary under "Electroplating" to see some of the other silverplate mark possibilities.
Regards, Tom