Civil Aviation Act Article 12

After the aircraft has been properly registered, the ROC nationality marks and registration number shall be displayed on a conspicuous part of the aircraft.
中文原文 民用航空法第12條
航空器登記後,應將中華民國國籍標誌及登記號碼,標明於航空器上顯著之處。

English translation for reference only; the Chinese text prevails. Not legal advice.