One of the UN's many delightful eccentricities is its internal United Nations Postal Administration, which was founded in 1951 and issues stamps than can only be used within the UN—even though, intriguingly, they're hugely popular outside of it. The UN recently issued its latest batch of designs, and they're great.
A bit of background: the UN is the only institution that's allowed to issue stamps that isn't a nation or territory, according to its website. The first postage stamps were issued in 1951, the same year the UN moved into its Oscar Niemeyer- and Le Corbusier-designed digs in Manhattan, and it was originally issued in dollars. Since then, the service has expanded to issue stamps in francs and euros, too, for use in its other offices.
Paradoxically, these stamps can't be used outside the UN administration but they're huge collector's items regardless, and have been for decades. Even though paper mail is no longer the primary way in which we communicate, the United Nations Postal Administration continues to issue new stamps on a yearly basis, using each year's designs as a way to call attention to global issues. This year's is endangered species of the ocean, and they were designed by Amadeo Bachar, an American artist who specialises in scientific illustrations.