|Signing "again/repeat" when she was young|
The reason I think sign language is so helpful for parents is because babies really understand it. At first they might just mimic your hand motions. But soon they learn that by hearing/seeing "repeat/again," you will play their favorite song again. It encourages them to mimic for a reason, and then be able to ask on their own. Before they are capable of speaking, they will be able to tell you what they want (or at least most of the time).
We started with signs like "more, repeat/again, and all-done". These were helpful when it came to eating table food, listening to music, or taking a bath. We always said the word with the sign, so it never replaced speaking for her. She learned both at the same time, but obviously she couldn't speak them so young.
As she got older, we added more relevant signs to her vocabulary as they were needed. Right now she knows more, please, all-done, thank-you, different, again, music, food, water, drink, milk, book, bowl, bacon, piano, computer, apple, poop (hey, it comes in handy), hungry, thirsty, cereal, happy.
I'm sure a lot of exceptional parents shy away from communicating through sign language with their advanced child because, well, they simply don't need it. "I already know what my baby wants, even before they try to speak." I know where they're coming from...to an extent. But coming from a stay-at-home mom who is with her kid 24/7, I even think it helps - especially during this babbling stage. Little Olive speaks some words clear as day - but then others I'm so clueless trying to figure out what she means. When she does the sign with it, then it all makes sense. Her spoken word for "music" sounds nothing like it. But when she waves her little hand across her forearm, I know she wants her songs. It's so adorable.
Here is a great link to help you get started or learn more:
I love this because it has videos for each sign and explains how to do it. Give it a try and see how quickly you can pick up some signs!