Without photos by OP it’s a bit of a guess still. But let’s look at Gilbert Tulley Sutterley (1863-1927) of G.T. Sutterley & Co. Philadelphia circa 1890’s-1910 or after.
Known: Manufacturer of select table items like coffee service.
Known: Seller of silverplate wares and more.
Known: Name found stamped on Plaza Pattern teaspoon (Reed & Barton, patented 1890) with topmarked personal letters of indeterminate origin. Plaza, though rarely seen, is known to carry marks which may be commercial user identities.
Found online materials:
Obituary is a descendant of Gilbert or his brother…George was re-used in the family.
No information was found on the possible partner Stewart, but perhaps this pre-dates the “& Co.” era. Nothing was found as to the demise of the company. (Mr. Sutterley shifts his address around, perhaps living along the Philadelphia-New York main line of the Pennsylvania Railroad?) Neither name came up under plater marks of Philadelphia on S.F.Fashions site.