What does "Shu" mean?

Well, it's the same as signing. Refers to the poems corresponding to divination and lottery. There are generally four sentences, which are the general statements that you want to predict the quality of things. Like Guanyin ling or something.

There are similar poems in some books of Buddhism and Taoism, which are more incisive.

There are also some personal works, which are hidden, unknown or unexplained, and are also hidden works that predict personnel or personal views on certain personnel, or are used to warn future generations.

Answer finished, I hope it will help you.