Whether you can write on a stamp depends on the situation. If a stamp collector collects a whole set, a whole year and a regular series of stamps, it is impossible to write on them. If there are words on the stamps, the appearance of these stamps will be damaged and become defective tickets, and the value will be much lower. However, some special stamps, with handwriting at a special time, have become extremely precious varieties. For example, the heads of some big countries sign their names or some famous sayings on some stamps related to political events. Such stamps are serious. For example, Chairman Mao signed his names "Mao Zedong" and "1959 10" on the stamp edition in founding ceremony.