I could not find an exact match to the marks you desribe in my American reference books. However, except for the cross in the shield I found a similar mark. Lehman Brothers, New York City, used a mark like this, but there were the letters EPNS in the shield. EPNS stands for ElectroPlated on Nickel Silver. Since your piece is electroplated on copper they would not have used the exact mark that is in in my scan. Founded around 1905, in business at least into the 1960's. Here's the scan of their mark:

Regards,
Pat.