What does it mean when sterling has SGP inside a triangle stamped on it?

The live draw sgp inside a triangle was the mark of Stavre Gregor Panis 1889-1974 who was a well known silversmith from Cape Cod Massachusetts.
His pieces were hand wrought and hammered and were intricately pierced. His wife Gladys 1900-2001 designed the pieces that he made. Their work is a fine example of the Arts and Crafts movement and are highly desirable. Prices varying according to pieces, jewelry, tea strainers, napkin rings, bookmarks, etc.