You are getting so good at your signs baby. I have always known when you try to say Mama or Dada, but to anyone else it wouldn't be obvious. Here you are clearly doing the sign for Mama! (Yes, silly Mommy recorded it sideways.) You understand much more than anyone gives you credit for, and I love to see you able to communicate back with signs. The only other one you know right now is "baby" for Liam. You can't do it yourself, but you smile big when I do it for you.
When I was in college I took American Sign Language as my foreign language. I had always felt a calling to learn and was never sure why. I considered maybe God was preparing me for something in my future, possibly a deaf child or loved one. So when you were born with perfect hearing but practically no vision, I was confused. I joked that I should have studied Braille instead. But God doesn't make mistakes, and He knew that sign language would be your only source of "verbal" communication. And you are using it so well already. It is so awesome to see how God works things like that out.