It may not make much difference. Some years ago, some hikers (in S. AZ) in trouble signaled with mirrors and successfully attracted attention. In due course, a team was dispatched to their locality and the problem was handled. In discussion afterward, the victims stated they were sending morse code, but all that was perceived down in the valley was random flashes. The persistence of the flashes was the determining factor in sending a team.

Pilots and ship captains might recognize an SOS, but John Q. Public is probably clueless.