Printer's mark
A printer's mark, device, emblem or insignia is a symbol that was used as a trademark by early printers starting in the 15th century. A more nuanced definition is provided by McKerrow (see below): that any picture, design, or ornament (not being an initial letter) found on a title-page, final leaf, or in any other conspicuous place in a book, and having an obvious reference to the sign at which the printer or publisher of the book carried on business, or to the name of either of them, or including the arms or crest of either of them, is—whatever its origin—that printer's or publisher's device.