Actually, when I'm not sure if an oncoming driver sees me, I wiggle my handlebar in order to wiggle my headlight. I'm pretty sure it works, as I've gotten some drivers to dip their high-beams that way.

Anyway, in general, bikes are pretty invisible on the road, so the more you can do to make yourself visible, the better. Use as many devices and techniques as you can, rather than looking for the best one device or technique.