In the 16th century Albrecht Dürer, one of the most celebrated artists of his time, marked his prints with a specifically designed logo of his initials. The logo quickly became internationally synonymous with his name (Dürer was one of the first artists to achieve substantial fame across Europe during his lifetime), and it was widely used to sell forgeries on the back of the "Dürer brand".

This is the logo (looking almost disturbingly modern), and you can see it here in one of his most famous works, Young Hare (1509). Neil McGregor's wonderful Germany - Memories of a Nation has an episode on Dürer and the "Dürer brand", which is well worth a listen!