I didn't know this before I read Sign but Nicaraguan Sign Language was developed when fifty deaf children were brought together with an intended focus on lip reading and alphabet signing. Instead, the kids came up with their own language.
Seriously, this blew linguists minds. The actual history and the discussions about how this worked and what it means is beyond fascinating.
Sign is less of a recreation of the development of Nicaraguan Sign Language and more of a tribute to it. It puts the players in the role of the children with one moderator as the teacher. It alternates between classroom scenes, where there is defined steps about communication and free form recess. Incidentally, the free form interactions at recess and out of class were crucial for the actual children to learn to communicate with each other.
One of the crucial mechanics, to my mind, is the compromise marker. If you feel you haven't been understood or you haven't understood, you take the marker and mark your hand. You will probably end the game with really hash tagged hands. This really forces you to acknowledge the difficulty in communication.
I also found it fascinating that the characters that were created for the game are more privileged than the actual Nicaraguan children who were part of the real initial class. The developers made that choice so that they would be more approachable.
Having people sit down and try to communicate with each other without using words is a far cry from what I usually think about when I think about LARP. As I said, it seems more like a form of therapy. It has to be a memorable experience.
I may well never play Sign but I'm glad I read it. It's an interesting exercise in communication and it made me start looking into the origins of Nicaraguan Sign Language.