I was discussing this with my sister, and she said she probably wouldnt recognise it and if she did it would probably be another ‘freak’ obsessed with lights just like me.
If I saw a SOS signal I would probably rush out after the completion of the 2nd cycle. You never know whats happening out there…
Investigate .
I’d definitely look into it. I wouldn’t go into full panic mode until I was sure it wasn’t someone just screwing around, but I wouldn’t ignore it either. Are here, most police are aware of S-O-S and will pull you over if you tap your brake lights in that pattern.
PPtk
I’d check it out. It’d probably take me more than two cycles before I recognized the pattern. I assume most flashes are random. Sitting on a mountain top looking down at a city of lights, I’d never pick out an SOS.
I would cautiously approach the area, and help if possible.
These days, I might be inclined to suspect that someone was just playing with their new flashlight.
Seriously though, it’s a situational thing.
depends where it’s flashing… if it is from the apartment i would hesitate, but if it’s flashing on top of the mountain or a deep valley, I will google local search and rescue team or call 911
I am a Veteran and was taught it in Boot Camp. I learned the SOS as Boy Scout though.
Three of anything, 3 shots, 3 fires, 3 blasts on a whistle…3 of anything is the emergency signal.
A few years ago, an old man was deer hunting and fell out of a tree and broke his legs. He used his rifle to fire 3 shots. After some time some other hunters heard him firing. They wondered if it was coincidence, however they went toward the sound of the gun and found him.
If I saw a morse code SOS I would move in that direction, if safe enough, while calling in backup from Civil Servants.
I'd investigate of course because I have a lot of experience.
Experience from watching a lot of detective tv shows. 
Would go check out.
If unable or cannot reach there - call help.
I'd go find out what kind of light he had ....
Like people said it would depend where it is . In an urban setting I'd probably call the police instead of knock on someones door .
if it were in the woods or boating I'd seek to offer aid and assistance
My first 2 lights had SOS on it, so I’ve memorised it as beep-beep-beep, beeeep-beeeep, beep-beep-beep.
Upon second thought I might not ‘rush’ over there, but I would definitely check it out.
Not to harp… but you memorized it incorrectly…
oops, I meant to add an extra long beep. I did memorise it as 9 beeps in total, but wrote down 8
I would probably investigate after seeing the full code flash more than three times.
SMS ? 
Save my soul, screw my shipmates!