I was surprised last night to learn my wife doesn't know how to signal SOS in Morse. Granted I was a boy scout for a few years, but I thought this was something everyone was taught. It's a sham that is apparently not the case.
if you're on a boat all day with a ham radio or such devices, sure it's useful to know. but in a big city or urban area with no general access to such devices? are you going to write dashes and dots on the wall???
not saying that it's useless to know. i learnt a lot of these things from my parents, and i would teach my children if i had any, but i can totally relate to people not caring about it in my area and finding it some niche interest for 'nerds' or so.
Even if the people searching the rubble don't know SOS, they will still recognize that it's not a natural noise.