Stamps
Stamps in the Discworld books
Since the re-opening of the Post Office, stamps have become something like the second official currency in Ankh-Morpork besides the Ankh-Morpork dollar (which is still solid coin made of a mixture of miscellaneous metals, probably). The advantage of stamps is that they weigh a lot less, take less space, and are a lot prettier. The Patrician's Palace estimates that a one-penny stamp, on average, changes hands twelve times, acting as a penny, before it gets affixed to a letter to redeem its value with the Post Office. The collecting of stamps swept over the city like a fever and replaced the rather popular collecting of pins. Stamps have become something like a status symbol. Every city (ex. Sto Lat and others on the Sto Plains), kingdom (ex. Lancre in the Ramtops), or guild wants its own stamp design, even though most of the cities and kingdoms do not have their own post offices.
Stamps as collectors items
The Discworld stamps are available as collectors items since 2004. The stamps are based on the descriptions in the Discworld books (especially Going Postal). All stamp designs get their OK from Terry Pratchett himself. The collectors' community is already quite large and active as the designers make sure they add a lot of special little printing errors that make certain stamps even more interesting. Some stamps are perforated by hand using an old perforator found at the Bath Postal Museum .