What does Dn 925 in my ring mean?

The marking "Dn 925" on your ring indicates that it is made of sterling silver, which is 92.5% pure silver (the "925" part). The "Dn" could refer to a specific brand, designer, or manufacturer, but it is less commonly recognized than the "925" mark. If you want to know more about the designer, you might need to research or consult with a jeweler.