That is cool if you are in fairly open high country. But these guys had climbed into the canopy of a tree, so both the sunlight, and the reflected light from th

That is cool if you are in fairly open high country. But these guys had climbed into the canopy of a tree, so both the sunlight, and the reflected light from the mirror could have been blocked by foliage. Smoke (or a flare) was about the only thing that could move above the treeline and be visible to an aircraft.