You assign prearranged meanings to visual signals to the soldier sending the signal and the soldier seeing the signal so both have the same understanding of what that particular signal means. Your commander will set prearranged meanings for pyrotechnics, smoke, and flashing lights. Panel markers are a series of cloth panels that you spread on the ground to communicate with aircraft. When standard cloth panels are not available, you can use field expedients such as clothing, branches, rocks, or snow. Information is usually taken from those publications and placed in unit CEOIs and SOPs.
Visual signals have some shortcomings that limit their use.
For example, visual signals can be easily misunderstood. Some visual signals are restricted during poor visibility such as at night or in dense terrain. Of course, at other times, they can be intercepted by the enemy who may, in turn, use similar visual signals to create confusion. Sound signals include the use of the voice, whistles, horns, weapons, and other noise-making devices to transmit simple messages over short distances. Also, like visual signals, sound signals are vulnerable to enemy interception and use.