People were talking about communication devices, and it reminded me of something I was thinking about before.
How many divers actually use sign language? Not signals, but the actual language. I would think it would be incredibly useful at getting across the more difficult concepts you might encounter. I know signals do cover all of the important "safety" things, but I'm sure you've come across enough other things where you'd either pull out a slate, write on your hand, or just wait until you're at the surface to communicate it.
My mom taught us kids the sign language alphabet many many years ago, I still remember most of it. I think if my dive buddy also knew it (and I had a refresher), it would probably be a pretty useful tool. I know I've had a few instances of trying to get across a fairly complicated point, and either spelling it out on my hand, or being forced to surface to explain what I wanted them to do.
Once again, I know you can get across almost any point with decent signals, but obviously it's not a full language. How useful would you think it would be to either learn sign language, or at least the sign alphabet? I was wondering if that was the type of thing I could suggest to my LDS as an optional class, etc.