Ground to air signals should be at least 10 metres long and 3 metres wide with 3 metres inbetween each signals. These signals can be made of anything, like branches, dark coloured soil or even burned trees. Just remember that they have to be big enough so that aircraft can see them. All search and rescue workers know these signals as they are recognized worldwide.
Unable to move
Serious injury
Going this way
Aircraft badly damaged
I do not understand
Require food and water
Indicate direction to proceed
Need map and compass
Need medical supplies
Need radio
Think safe to land here (broken triangle is aircraft taking off)
Negative
Affirmative
Yes (same acknowledgement as affirmative)