I think it depends who you expect to see your signal.

Everybody knows what SOS means, and what to do about it (with the exception of a small number of people working near a certain resort in BC, but I digress).

But if Joe Average is out skiing and he sees a big X in the snow on the slope opposite, is he likely to do anything about it?

If you left a trip plan, and you're overdue, then you know that SAR is likely to come looking for you. If your buddy broke his leg, and you're stranded, and you're not overdue ... you may be relying on Joe Average to interpret what your signal means.