Hi Patti,
This is not Monart, which was made in Scotland. These FBS marks are presumed to be that of US based importer or retailer. The mark, sometimes as a label, has been found on Czech, French and Italian glass. Hopefully someone can identify who made yours and we might get to a better date. Currently it could be anywhere from 1930's to 50's and no-one has come up with any possible identity.
Mostly the pieces with this mark have appeared in the US