What won’t they be able to tell you is probably a better question! Essentially any of the 350 signs tailor selected for the baby sign language course will be fair game for your baby to sign back to you. They will be able to tell you when they are hungry, thirsty, tired, hurt, interested in starting conversations about things of interest, when they hear birds or see animals such as cats and dogs or zoo animals in photographs or on prints on their clothing. Be prepared to be amazed by exactly who much your little guy or little girl really understands about the world. See the world through their fresh eyes.
There’s really no limit to what a baby can sign. Some parents start signing early and focus on manners and emotions trying to build emotional intelligence. This will be key in controlling their moods and tantrums. Manners are useful in creating children who have a sense of appreciation and whom are less demanding. Labeling animals, things and activities is amusing to other parents who focus more on fun. Naturally the best balance comes from teaching a variety of signs. Remember that these signs will form the foundation for you child’s vocabulary as they add verbal words and naturally whatever you focus on in either department will matter to them in the long run. No doubt their interests will evolve around yours as well so whatever signs you feel are appropriate to your family are signs you should teach.