I believe this is probably a coaster for a drinking glass or bottle - but it's just too pretty to hide, and would love to hold your rings and jewelry instead! Measures about 3 3/4" across the rim.
This is a 1940s or 50s vintage piece, a ruby glass bowl with silver plate exterior. It's marked F B Rogers (which eventually became International Silver). Silver is very tarnished though doesn't look terribly worn.