No, that is a myth. In fact, it can have a positive impact on your child’s communication.
No research to date supports that teaching baby signs is detrimental to speech development. Very early on, learning baby signs can give your child another means of expressing wants and needs besides just crying. Essentially, it can help babies to become better communicators and just might spare some tantrums along the way. And what parent wouldn’t want that?
In addition to teaching an effective means of requesting, baby signs is also a great way to expand your little one’s naming vocabulary. You will be teaching him to express the names of items that he otherwise would not be able to pronounce at such a young age. Teaching a visual gesture along with a word seems to help many children learn to verbally say the word faster.