Play a gypsy and tell fortune to his guests and Jane. How does Jane recognize him?

This is described in chapter 19. Jane Eyre was very alert from the very beginning, suspecting that this was a disguise;

Jane loves to know that gypsies and fortune tellers don't talk about their ideas like this old-looking woman.

Jane Eyre noticed the gypsy's disguised voice and her eagerness to hide her face.

Jane suspected him, but at first she thought it was Grace Poole, not Rochester. ...