Thank rafowell, not me!

In my experience, spotting a person from the air (as opposed to the wreckage of an aircraft) is extremely difficult, at least in our local terrain. I would suggest that the single most important thing, rather than some specific signal, is to wear or have available some bright, contrasting clothing. An orange jacket or vest stands out from miles away.

Years ago, a series of experiments were conducted in Arizona to attempt to quatify the POD (Probability Of Detection) of a subject from a helicopter. I believe hikermor may have participated in those experiments? The studies are available on the saraz.org Documents page. They did a Mountain Searches experiment, and a Desert Searches experiment. In my experience here in Alaska, their PODs were quite optimistic. That's probably due to the fact that we tend to have a lot more brush and ground cover.

My bottom line advice is if you want to get found from the air, wear some bright orange clothing!