What is the meaning of the signboard in the "cloud-like weather sign" in "Seeing the weather from the clouds"?

3. Interpretation of "signboard" in Zhu Yongxi's "Seeing the weather through clouds": ontology: cloud; Vehicle: signboard. Similarities: Both of them have indication function. But the signboard is more obvious, close to life and easy to understand. Therefore, the signboard is used as a metaphor, which is vivid. The word "signboard" is used figuratively here.