Got signal mirrors and smoke bombs.... never tried to communication with them except decades ago, just for fun.... If I remember correctly, we didn't have a good signal system... that is we could see the signals but changing them into meaningful messages was tough.
ok, I found one of my follow up links... http://www.equipped.com/signal.htm
I found this page after watching a survival expert take a handful of folks into the grand canyon for a survival exercise (show was on Discovery Channel).
Interesting read...tells what doesn't work and what works "better".