How can you signal for help?

If you are lost in a island you can use a mirror to flash a sunlight signal over long distances if you see a plane or people in the distance, or make fire with green and wet wood to send up ample smoke during daylight.
https://noticeboards.netlanguages.com/phpBB3/
https://noticeboards.netlanguages.com/phpBB3/viewtopic.php?f=6&t=18278