Laythinehanduponthymouth - This was the token of silence. The god of silence, Harpocrates, is represented on ancient statues with his finger pressed on his lips.
SDA Bible Commentary (limited)
Volume 1-7
19. Upon thy mouth. The laying of the finger on the lips is one of the most universal of gestures (see Job 21:5; 29:9; Prov. 30:32).