Printers' Marks

Here is a great reference from Project Gutenberg on Printers' Marks.

The Project Gutenberg EBook of Printers' Marks, by William Roberts

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Title: Printers' Marks
A Chapter in the History of Typography
Author: William Roberts
Release Date: June 1, 2008 [EBook #25663]
Language: English
Character set encoding: UTF-8
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THERE are few phases of typography open to the charge of being neglected. An unquestionable exception occurs, however, in relation to Printers’ Marks. This subject is in many respects one of the most interesting in connection with the early printers, who, using devices at first purely as trade marks for the protection of their books against the pirate, soon began to discern their ornamental value, and, consequently, employed the best available artists to design them. Many of these examples are of the greatest bibliographical and general interest, as well as of considerable value in supplementing an important class of illustrations to the printed books, and showing the origin of several typical classes of Book-plates (Ex-Libris). The present Handbook has been written with a view to supplying a readable but accurate account of this neglected chapter in the history of art and bibliography; and it appeals with equal force to the artist or collector. Only one book on the subject, Berjeau’s “Early Dutch, German, and English Printers’ Marks,” has appeared in this viii country, and this, besides being out of print and expensive, is destitute of descriptive letterpress. The principle which determined the selection of the illustrations is of a threefold character: first, the importance of the printer; secondly, the artistic value or interest of the Mark itself; and thirdly, the geographical importance of the city or town in which the Mark first appeared.

If I've correctly interpreted the publication date, it is 1893. He seems to have much more interest in later or "contemporary" marks than in the incunabula, but there is a fair share of those as well. It is an interesting read with lots and lots of samples.