From Discworld & Terry Pratchett Wiki
A guild which was long opposed to movable-type printing and was therefore exercised when William de Worde and some Dwarfs set up a printing press during the events of The Truth. They soon saw the printing on the wall, however, and expanded the name to the Guild of Engravers and Prínters, whose current President is Ronald Carney.
In Interesting Times, Rincewind notes "some of the craftsmen in the Engravers' Guild could engrave their name and address on a pinhead", which is probably why paper money has never before been introduced to Ankh-Morpork. After seeing what Owlswick Jenkins is capable of as regards forgery, both Moist von Lipwig and the printing contractors Teemer and Spools are resolved that there have to be other safeguards introduced into the new paper currency.
Moist has heard that imps can be built into paper by a thaumatalogical process. He believes the Unseen University will be only too glad to help, in return for the new five-dollar notes bearing a portrait of an eminent wizard, like, say, Mustrum Ridcully.