what gesture does the man make to Hester that suggests he knows her in chapter 3?

he raised a finger to his lips;

"After a brief space, the convulsion grew almost imperceptible, and finally subsided into the depths of his nature. When he found the eyes of Hester Prynne fastened on his own, and saw that she appeared to recognize him, he slowly and calmly raised his finger, made a gesture with it in the air, and laid it on his lips."