The above technique works best with a compass sighting mirror, or any specialized, commercial or military signal mirror. It also works, to lesser degrees, with any object that will reflect sunlight. Try using a watch crystal, cell phone screen, knife blade, and similar objects.
Experiment with different target objects around you, which forces you to use different mirror-to-sun angles to achieve a sunspot.
Practice the above technique with co-workers or acquaintances on the ground under controlled conditions. Do Not practice on aircraft or vehicles! The flashes are bright and can be blinding.
During an actual emergency, when signalling aircraft, cease signalling when the aircraft passes overhead and clearly acknowledges it has recognized your position. The flashes may impair the pilot or air crew’s vision.