Ground-to-air signs are used in times of distress. They are an internationally recognized emergency code that you could use anywhere and pilots and rescuers will understand you. Try to find a reasonably flat, clear area and make the symbols out of groundsheets, wood, stones or any material laid on the ground with a color that contrasts with the background. You could turn over sods, or scrape the signs or their outlines into the ground or snow.
Other distress signs
During darkness, build three fires in a triangle formation. This is an international distress signal. (Avoid starting a forest fire!) Alternatively, use a flashlight to send an SOS signal. This uses Morse code and is three short flashes followed by three long flashes followed by three short flashes.
During daylight you can create three columns of smoke. This is also an international distress symbol. You should make white smoke against a dark background and vice versa. To create black smoke, add rubber, plastic or oil-soaked rags to the fire. (This is dangerous so be careful not to make your situation worse than it is already.) To create white smoke, burn green leaves, moss or sprinkle your fire with water.
On a sunny day mirror flashes can be reportedly be seen 70 miles away under normal conditions in most environments.
In tree cover, put your distress sign on top of a tree. Use bright colors, such as sleeping bags or clothes.
On mountains, three long blasts of a whistle in quick succession, repeated at one-minute intervals will signal distress. The acknowledgement is three blasts followed by a minute’s silence, and then repeated. In hunting areas, if you hear three timed shots – pay attention, there could be a hunter in trouble.