I am not SAR. That said, I can guarantee you that I would most likely ignore a steady strobe, but if I were to see an SOS I would definately investigate it. If strobes are becoming that common I may treat them the same from now on.

Edit: Come to think of it, I saw an activated strobe on my way to work this morning. It was attached to a bicycle that somebody was riding along the road in the dark. It was very effective as a warning to other drivers, but the rider did not appear to be in any distress. Given such uses, I think I'd stick to SOS for a distress signal. Less chance of it being mistaken for something else.