No. Sign language is a type of Augmentative Communication. Signs can actually help a child to talk. Studies have actually demonstrated that children as young as 9 months have developed a large sign vocabulary, much earlier than their spoken vocabulary, and that these same children spoke earlier than same aged children.
Talking is a very complicated process requiring the child to be able to know what a word means, know when it is appropriate to use that word, remember how the word is pronounced and then physically being able to put the sounds together to produce the word.
Sign language helps a child understand what a word means because it is visual and can be “seen”, rather than just sounds in space. Similarly by observing others using signs in conjunction with the spoken word, the child learns when the sign/word is to be used. This then allows the brain to focus more on the co-ordination of all the muscles required for the pronunciation of the word.
The added bonus is that during your child’s learning of word pronunciation (which can sometimes take months for this connection to occur) they have a way to communicate with you that is not as physically challenging, thereby reducing everyone’s frustration!