Quick answer is anytime! You can start signing to them now when you talk, but they most likely won’t start responding with signs until at least 8 mo.
This book is great! Baby Sign Language Made Easy: 101 Signs to Start Communicating with Your Child Now (Baby Sign Language Guides) https://a.co/d/ceK64YW
Re: Sign language!
This book is great!
Baby Sign Language Made Easy: 101 Signs to Start Communicating with Your Child Now (Baby Sign Language Guides) https://a.co/d/ceK64YW