postage stamp, government stamp affixed to mail to indicate payment of postage. The term includes stamps printed or embossed on postcards and envelopes as well as the adhesive labels. The use of adhesive postage stamps was advocated by Sir Rowland Hill; it was adopted in Great Britain in 1839. Zürich (Switzerland) and Brazil issued stamps in 1843, and by 1850 the custom had spread throughout the world. Although the postmasters of several cities had previously issued provisional stamps, the first U.S. official issue was in 1847. Stamps are usually printed from engraved steel plates or cylinders, or by typographic or lithographic means. Besides regular stamps, which date from 1847, the U.S. government also issues commemorative stamps, which celebrate events or persons; memorial stamps in honor of officials who die in office; airmail stamps; and special stamps, e.g., special delivery, postage due, and revenue stamps. Self-adhesive, or "self-stick," stamps were introduced in the United States in 1974 but were not successful; they were reintroduced in 1994 and now comprise the vast majority of U.S. stamps issued. The computer age came to U.S. postage stamps in 1999, when, as PC Postage, they became available for purchase and downloading on the Internet. The popularity of philately has led some governments to issue a great many stamps, usually commemoratives. Some small countries, like San Marino, receive much of their revenue by issuing stamps attractive to collectors.