Since both my wife and myself already had the benefit of knowing sign language when our daughter was born, we decided that we would teach her how to sign from infancy. What a good decision that was!
There is a ton of research that shows the many benefits of babies learning sign language, such as being able to communicate with them at a much earlier age, which reduces tantrums and frustrations (for both baby and parents).
One of the ways we taught our daughter sign language was the Baby Signing Time series by Rachel. Her vocabulary grew much quicker than we had ever expected, as well as her being able to recognize written words. She is currently 19 months old and can say and sign her alphabet, identify words and numbers. She already has a vocabulary of hundreds of words, phrases, and signs.
If you are a new parent or have a young one at home, we would wholly recommend the Baby Sign Language videos from Signing Time. If you would like, you can check it out with the link below.