Because the UN is an international organization, its stamp must bear symbols that will be recognized universally. Besides the beauty of the design, the UN Design Committee must consider the political implications of any symbolism used. Naturally none of them can stand for anything contrary to the standards and principles of the United Nations, nor can they represent any one culture, religion, or race.
It was the Design Committee’s suggestion that the official five languages—Chinese, English, French, Russian, and Spanish—should be used on as many of the stamps as possible. This was the origin of the “five-language border” which has become characteristic of UN stamps.