it could be Libby.
It is DEFINITELY Libbey Glass. Libbey is the only glass manufacturer that marks their glassware with the notorious Libbey script L
Robert L. Glass was born in 1932.
Jimmy L. Glass died in 1987.
Mark Glass was born on November 12, 1947, in St. Louis, Missouri, USA.
Mark L. Taylor was born in 1954.
Mark L. Schneider was born in 1941.
Mark L. Young was born in 1991.
Mark L. Knapp was born in 1938.
Mark L. Lester was born in 1946.
Mark L. Grover was born in 1947.
Mark L. Walker was born in 1941.
Mark L. Tidd was born in 1955.
Diamond is harder than glass, so a diamond will 'mark' glass. Glass-cutting takes place when the worker uses a diamond-tipped tool to mark the glass along the cut line, then applies pressure to the glass on both sides of the mark. Glass-cutting tools are tipped with industrial diamonds, which are 80% of all diamonds mined.