Legally, in the United States, if an item contains 92.5 percent real silver, it is marked as sterling silver. Real silver is also indicated by a .925 marking. To determine if an International Silver Co. dish is sterling or plated silver, check the back of the dish for authenticity markings.
If the word silver is used without the sterling designation, the item is most likely silver plated. Another way to tell the difference is to perform an acid test. Alternatively, a testing stone can determine silver content. For 100 percent accuracy, the item should be brought to an expert in silver collectibles to determine its value.