Hello, I believe this might also be a Felsenstein & Mainzer mark. This one with “F&M” over “N” (N presumably for Nurenberg) inside a circle.
It was on a Berlin commemorative “plated” stein” (bronze/copper colour showing on high places). A website, steinmarks.co.uk, suggests F&M started as late 19th century pewterers before continuing as designer procurers and wholesalers of pewter and other metal products. That was until just before the end of WWI when Gebruder Bing purchased the concern. F&M‘s product range still continued to manufacture and sold into the 1930’s. (This is a similar summary to that referenced earlier in this post)
https://www.925-1000.com/forum/viewtopi ... 27#p137927
Fishless