Brunette Girl Posing On The Mirrors

Signalling
With the sun as light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to 60 kilometres on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.
Mirrors can also be used for rescue, especially to attract the attention of search and rescue helicopters. Specialised signalling mirrors are available and are often included in military survival kits. Remember that pointing an ordinary mirror directly at the intended receiver will not work if the sun is too far off to the side. The mirror should be pointed directly between the light source and the signal target.