printer's mark is a device used for visual identification of the printer, his business and, many times, his family. It could be considered as the first form of copyright to protect the intellectual contents and to guarantee the quality of the book. In the beginning of the mid-15th century, these devices were very simple designs. However, by the mid-16th century, they had evolved into a serious art form with ornate and complex patterns. There are fine examples of these marks in the dome of the Main Reading Room above the College Library Reference Desk.