I think it is a great way to communicate with babies, especially for new parents. I have used the sign language training with both my kids. I started teaching them as early as five months. Once they are ready they will start to sign back. I used very basic signs like More, Done, Sleep, Hungry and Change.
I taught my babies to open their fingers keep the palms up.
I taught them to flip open hands upside down.
Close the eyes and keep the hands in “Namaste” position.
Make circular motion with hand on the belly.
Point to the diaper to say that they need a change right now.
All the best.