Silver? Wine or Champagne coaster hallmarked

My silver knowledge is terrible. This is hallmarked so my thought is silver but I am unsure. Anyone recognize the hallmark? 7" across. I purchased it at high end estate sale. Lined with felt on the bottom, but I cannot tell the material used inside.
Any help would be appreciated.

 

That's not a hallmark, it's a maker's mark for Corbell and Co, a maker of silver plated goods.

See their entry on the page in this link. https://www.925-1000.com/silverplate_C2.html

 

yup..

 

These wine coasters typically had a cork liner on the inside but those almost always get lost.

 

The letters are EPM... Electro Plated Metal.