Negotiable Instruments Act Article 9

An agent who signs a negotiable instrument without expressly indicating that they sign on behalf of the principal shall be personally liable for the instrument.
中文原文 票據法第9條
代理人未載明為本人代理之旨而簽名於票據者,應自負票據上之責任。

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