Always have a sighting compass avec mirror, so presume (never good, presuming) I could aim it off my thumb and flash a plane or heli. Of course, it must be clear and the sun at the correct angle. Which happens, sometimes.

Vaguely recall Colin Fletcher describing his travails signaling a resupply plane in "The Complete Walker". Wasn't it his white tarp that the pilot finally saw, rather than the fire or mirror?

My bottom line: there's no one method that works for all typical situations, so you'd best have at least three tricks up your sleeve.

Cheers,