Established in 1874, the Universal Postal Union (UPU), with its headquarters in Berne, Switzerland, is the second oldest international organization worldwide (after the International Telecommunication Union, ITU); it coordinates postal policies among member nations, in addition to the worldwide postal system, and became on 1 July 1948 a specialized agency of the United Nations.
The United Nations is the only organization in the world which is neither a country nor a territory that is permitted to issue postage stamps. It is also the only postal authority to issue stamps in three different currencies, namely U.S. dollars, Swiss francs and Euro. The first United Nations stamps were issued in U.S. dollar denominations on United Nations Day, 24 October, in 1951. UN stamps have illustrated the aims and achievements of the United Nations and its family of organizations.
International days are occasions to educate the public on issues of concern, to mobilize political will and resources to address global problems, and to celebrate and reinforce achievements of humanity. The existence of international days predates the establishment of the United Nations, but the UN has embraced them as a powerful advocacy tool. We also mark other UN observances.