i tried this with my first son (now 13) and , i believe, because he could communicate, he was one of the most contented , happy baby, you would have met.
My second son came along 6 years later ( now six) and i didn,t think the signing was a cause of my first sons nature so did not do it with son two. He was the most unhappy, discontented baby/toddler ever!!!!!!!!tantrums and tears galore.