Ask for a magic trick. I've seen fortune tellers do this

Ok, I'll tell you, first hide the pencil refill on your thumb, then lie about writing it, but the paper is blank, and then wait for someone else to report it before writing it. Be careful to hide the pencil lead on your thumb, and it is best to cover it with paper.

Shit, they all copied mine.

Another change is to write it in your pocket so that others can't see it. As for the technique, you should take a thicker notebook and write it in your hand.

Just use a refill. It's safer to put it in your pocket, and then you can put it in your pocket so that others can't see it.