The ability to attract others' attention could be the deciding factor in whether or not you survive any given ordeal. Whether you are lost in the wood, trapped on an island, or trying to establish a line of communication the ability the signal others is of extreme importance. There many different methods and devices for accomplishing this, some better than others.
There are certain concepts that are known worldwide by search and rescue teams as well as anyone interested in preparedness and survival.These are some of them.
Rule of Threes
When you want to create a visual signal to your rescuers, you should alway take into account the rule of three. Whenever three objects are seen, this suggests that distress and that someone need to be rescued. These objects could be signal fires, rock formations, or just about anything else obviously man-made.
The SOS is the international Morse code distress signal. It consists of three dits, three dahs, then three dits without any pausing in between. It has come to be recognized as "Save Our Souls", although this was infact not the original meaning. An SOS can be created using light or sound. Devices such as signal mirrors, flashlights, whistles, smoke signals, or just about anything you can think that creates a visible or audible signal.
If you are in visual range of potential rescuers and wave to get their attention, always use both hands flailing wildly. A single arm wave could easily be mistaken as a greeting, two arms is far more likely to get the attention you want.
There are many different signaling devices, this is a list of some of them.