In addition to mama, daddy or dada is another common first word among babies. Until you baby can talk, however, you can teach your baby the sign for the words father, dad, daddy, and papa in baby sign language with the following description and video. The sign is identical in American Sign Language for all four English words.
Father, Dad, Daddy, Papa
Form an L with the hand. Tap the thumb against the forehead.
Beyer, Monica. 2006. Baby talk: A guide to using basic sign language to communicate with your baby. New York: Jeremy P. Tarcher/Penguin.