Their messages have been carried from sender to addressee - by horse or camel, by train or plane, by bicycle or on foot. And people have paid for this service for over 150 years by simply sticking a postage stamp on the folded-up letter, or on its envelope, or on a postcard.
Many stamps portray the country's king or queen.
Some bear colourful flags or crests, or national symbols like a swastika, red star, or chrysanthemum. Once people started collecting stamps, the world's postal administrations began issuing colourful designs that portrayed their own history, culture, geography, famous people, fairy tales - any theme that pleased their own people and was good publicity for the country.