Regulations Governing the Handling of Mail Article 19
Postage stamps or other postage paid symbols shall be neatly affixed on the cover of a mail item without overlapping; any postage stamps or other postage paid symbols that are totally or partially covered shall become invalid.
中文原文 郵件處理規則第19條
郵件上之郵票或其他表示郵資已付之符誌，應逐一分開端正勻貼，不得重疊；其被掩蓋者，失其效用。