The Plains Indian Sign Language, PISL. Is a endangered language loosing out to ASL. This book shows many of the signs, and while I can't verify how accurate they are protrayed and if you'll learn to use correctly, I feel sign language of any nature is better learn visually than through a picture book. It does show how different these signs are from ASL, and sadly like many Native American Tribe verbal languages what we are loosing in culture and history.