After you’ve come across enough people, you’ll come to hear the main objection to teaching a baby to sign.
“Won’t teaching your baby delay speaking?”
I’ve heard this many times and from many different people. My answer is always the same. Does crawling inhibit walking? The answer of course is no. Both are milestones and both assist a baby in their development. Whether or not a baby learns proper signing, he or she will still sign. They’ll pick up our body language signals such as waving bye, pointing to draw attention, clapping to show appreciation and excitement, shaking the head for no, and nodding for yes, stomping to show frustration and so forth. Later in life your toddler will even start using their hands to help them describe things. If you live in a country who use gesticulation prominently, they’ll adopt these signs even sooner.
The fact remains that our hands likely played a key role in communication throughout our ancestry. Before our vocal cords and voice boxes were attuned to speaking, we likely used grunts, screams, and so forth to express ourselves. While we’ve come a long way from primitive emotional communication, our hands still form a rudimentary means of expression. So while babies can’t yet talk, we might as well facilitate their hands to carry the load in the meantime. Besides, if we don’t refine a babies nonverbal skills, they’ll be far less meaningful and clear to the world. Keep in mind, ASL (or whatever official sign language you choose) is universal to other caregivers too!