The printer's mark was a part of the colophon in many early incunabula. The colophon appeared at the crowning part, or end of the early printed books. It included the title of the book, the name of the author, the printer's name (sometimes device only), the place and date of printing, and not infrequently, notes invaluable to modern scholars -- edition, patron, etc. In other words, the colophon gives the information we now find on the title page. The printer's mark was a kind of trade mark. It came to be a token of a master's pride in his work.
Main Entrance: Printer's devices on the vestibule entry sides
Left - Bernardino Benali, ca. 1497, used this sign of St. Jerome in a printing of the sermons of St. Bernard, Venice, Italy.
Right - Bernardino de Ferrari, called Stagnino de Trino used the heart and cross sign of St. Bernard, ca. 1490, Italy.
Mezzanine: Printer's marks on the glass panels on the west side (left to right):
The two shields suspended from a branch are Fust and Shoffer, printers of Mainz, Germany, ca. 1457 (contemporaries of Gutenberg.)
Globe, shield, and cross of St. Albans Press, ca, 1483, a monastery in England.
The anchor with dolphin adopted by Aldus Manutius, the elder, ca. 1482, Italy.
The elaborate bordered device is that of William Caxton, ca. 1474, England.