An International Silver marking marks a piece of silver-plated silverware produced by the International Silver Company. The marks may take different forms, but they are interpreted the same but often consist of "International Sterling" or add "925" to indicate the piece was indeed sterling.
The simplest and one of the most widely distributed International Silver markings, "I S" was simply the company's initials. The International Silver Company was actually a group of independent silversmiths from the New England area, many of whom had already made their mark in the silver industry in the late 19th century. When they joined together to form the International Silver Company in 1898, they formed the world's largest manufacturer of silverware.
Some of the larger, better known companies that were part of the new International Silver Company continued to use their markings or modified them with the seemingly ubiquitous "I S" somewhere within. As the marks for sterling silver could only be applied to sterling pieces made of 92.5 percent silver, the company changed the mark to "International Sterling" for them to indicate the silver content and left the "I S" for electroplated pieces.