Smoke signals is one of the oldest forms of communication, and is a form of visual communication used over a long distance.
On an elevation the signaler built a fire of material that would make heavy smoke, such as damp grass. By passing a blanket across the fire, he created separate puffs of smoke that conveyed information by their number and spacing
Around 150 BC, another system was created, it was a more complex system of alphabetical smoke signals. By converting greek alphabetic characters into numeric characters, it was devised to enable messages to be easily signaled by holding sets of torches in pairs
http://history.howstuffworks.com/native-american-history/smoke-signal.htm
