Printer’s devices are symbols or vignettes that identify the printer or press, acting as their trademark. Fust and Schöffer were the first to use such a device in 1462 and by the end of the 15th century the idea was firmly established. Ranging from simple designs based around initials, to much more elaborate engravings, devices were useful and popular for several hundred years. Originally conceived to help prevent against the pirating of books, the opportunity to produce ornamental designs was soon grasped. Placed in the colophon or on the title-page the devices advertised who was responsible for the book. In the modern period the printer’s device has mainly been replaced by publisher’s logos, and even by the end of the 19th century they were not utilised to a great extent. 
A vignette was found in the Rare Books Dept. of Cardiff University, which shows a (garden?) snail, the somewhat stylised shell seen in quasi-lateral view from the front, its head lifted upwards.
This snail image appears to be a printer’s device for the Bronze Snail Press, a privately-owned press that was active in the 1930s (Ken Gibb, Cardiff University, in litt., 14.i.2014).