在语言学中，字母序列'signifier'代表狗的概念。

In linguistics, the letter sequence '___signifier' represents the concept of a dog.

在语言学中，单词'树'是一个符号，代表了现实中的植物。

In linguistics, the word 'tree' is a ___signifier that represents the actual plant.

他独特的红色领带成为他在会议上最明显的身份标识。

His distinctive red tie became the most noticeable ___signifier of his identity at the conference.