The fad of "teaching your baby to sign" came along after Jumper Girl started talking. I thought of it as another example of pretentious parenting (or hyper-parenting).
Now I may have to modify my stance a bit--both informal and formal gesture use may help with language development. Check out the article at the Child Psychology Research blog:
The authors discussed research showing that the use gestures by infants is a good indicator of later language development. Gestures can differentiate between typically developing children and those with language delays at the age of 9-12 months. And later, they can differentiate between children with different developmental delays such as Down’s Syndrome and Autism. Children with good prelinguistic gestural communication at 14 months usually have better comprehension at 24 and 42 months than those who do not. Thus, assessment of gestures can help differentiate a “late-talker” from a true language delay. Furthermore, symbolic play which requires gestures is not only associated with cognitive skills, but it has also been shown to predict later language skills. Gestures play a large role in symbolic play from pretending to drink to indicating night-night by closing eyes and putting hands against the head.
The authors then discussed the developmental trajectory of gestures and the number of behaviors within the use of gestures that are important. Typically 12-month-olds use one gesture per minute, 18-month-olds use two, and 24-month-olds use five gestures per minute. The type of gesture also changes with development. Twelve month-olds use mostly vocalizations or gestures, 18-month-olds begin to ad words, and 24-month-olds use mostly words. There are also specific gestures that are important markers or predictors of normative development. For example, pointing has been linked to better language development, especially receptive vocabulary. The extent to which a gesture has communicative function plays a role as well, so that the more intent is embedded in the gesture, the better the outcome for language development. Another important landmark in communication is when gestures are paired with eye gaze and vocalizations. In fact, in normative development we expect a child to move from eye gaze and vocalization to gestures and vocalization, and then to gestures and words. As you can see, just as language follows a developmental path, so do these prelinguistic sounds and motor movements.