Curious to know how accurate this article is:
The Perfect Master speaks : Are there really “lost cosmonauts” stranded in space? - The Straight Dope
I think it likely that a military officer in the 1950s or '60s would know Morse code. Also, ‘SOS’ was chosen because repeating groups of three is a traditional distress signal. (e.g., firing three shots in the air, lighting three fires in a triangle, three dots/three dashes/three dots.)
Oh, and to adress your question : yes, of course. Morse code was created in the mid 19th century, and was still a required knowledge for all commercial and military pilots as recently as the 90s. It was also widely used in maritime communications. Heck, everyone who ever operated a radio had to know Morse code 
How does Morse code work with Cyrillic?
there is a version Morse code for non-Latin alphabets - Wikipedia
SOS became the international signal of danger after a mnaritime accident in 1912. So any one who could send Morse code would know SOS. Before 1912 the signal was CQD.
I may not be an expert on physics but neither the ‘stranded in an expanding orbit’ line nor the ‘at a single point and slowly moving away from the Earth’ descriptions seem to make sense.
How can an orbit be expanding unless the craft is actually accelerating? That’s not stranded. They would only have to turn off their engines to stop the expanding of their orbit. And it wouldn’t take much thrust to begin re-entry.
Similarly, if the spacecraft was not in orbit but was moving away, it would have to be continuously putting out a great deal of thrust to fight the constant pull of gravity, and could come back down relatively safely by simply cutting off thrust (re-entry is only hot because it normally happens at orbital speeds)
Yeah, this not a good article and the source is questionabe. Skeptoid has a better one here that addresses some of the more outrageous claims:
He claims that the those sounds couldnt be heartbeats as they were never broadcasted as pings.
I didnt know SOS was standardized in 1912. Thanks.
Who would the cosmonaut have been signalling to? He knew that he wasn’t going to be rescued, so why go to the trouble of sending a distress call that he knew couldn’t possibly be answered? OK, if you’re ditched somewhere on Earth, no matter how remote, it would be worth a shot - someone might be listening and come to your aid - but in space, in 1961? Colour me sceptical.
Im sure if you think youre going to die then youre probably not being rational. Or you may think youve landed in the sea and are bobbing there waiting for rescue. Who knows. It all seems pretty unlikely regardless.
I wonder if these brothers were simply being punkd by a 1960s Ashton Kutcher. How hard would it be to for someone on Earth to broadcast something on a frequency they were listening to? I dont think they would be able to tell if the transmission was from a local source. I wonder if there’s a way to analyze them today to see if they share or dont share any audio characteristics.
Technically SOS was actually standardized effective July 1, 1908 by the 1906 Berlin Radiotelegraphic Convention, although the Marconi companies resisted the change, and didn’t completely give up their own distress signal, CQD, which they had adopted in 1904, until after the Titanic sinking in 1912. Germany had been the first to adopt the SOS distress signal, effective April 1, 1905.
More damning than the SOS is the claim that they used LED’s in 1962:
While LED technology had been around since the 1920’s, the first practical LED’s weren’t produced until 1962, and they cost over $200 each. It is just not likely that hobbyists used them in their cobbled together command center; I doubt that even NASA was using them at that time.
SOS was around before, but it was not adapted as the international signal until after the Titanic. That event caused many changes in international maritime law.
All it need be doing is going quicker than orbital velocity 
Service Regulation XVI of the 1906 International Radiotelegraphic Convention, reads: “Ships in distress shall use the following signal: …—… repeated at brief intervals. As soon as a station perceives the signal of distress it shall cease all correspondence and not resume it until after it has made sure that the correspondence to which the call for assistance has given rise is terminated. In case the ship in distress adds at the end of the series of her calls the call letters of a particular station the answer to the call shall be incumbent upon that station alone. If the call for assistance does not specify any particular station, every station receiving such call shall be bound to answer it.”
This convention was signed on November 3, 1906 (effective July 1, 1908) by Argentina, Austria, Hungary, Belgium, Brazil, Bulgaria, Chile, Denmark, France, Germany, Great Britain, Greece, Italy, Japan, Mexico, Monaco, Norway, the Netherlands, Persia, Portugal, Roumania, Russia, Spain, Sweden, Turkey, the United States and Uruguay – i.e. the vast majority of the navigational countries.
Last year marked its 100th anniversary–see, for example, Today is 100th anniversary of ‘SOS’
You might as well ask why a soldier who’s guaranteed to die go over the top of the trench into machine gun fire. Why a man stranded at sea would struggle to not drown, and choose to starve and dehydrate rather than just letting go. You do everything you can, no matter the odds, because that’s what umpteen generations of organisms did who by remote chance ended up surviving, and passing that behavior down.
The ones who “just let go” didn’t.
Not quite: They would need to have been going at faster than escape speed, which is sqrt(2) times circular orbital speed. Anything in between circular orbital speed and escape speed will put you in an elliptical orbit which recedes away from Earth for half of each orbit, but then comes back down every time.
All true, but once you hit near-Earth escape velocity - c25000 mph - you will still decelerate as you head away from the Earth, and you could very well end up moving “slowly” away from the Earth without need for any more motive power. Something very strange would have had to happen to a 1961-vintage spacecraft for this to happen, though. A mission intended to achieve orbit wouldn’t end up hitting escape velocity plus a little over purely by accident. :dubious:
Not buying it: this isn’t just some panicking mook reflexively flailing his arms and yelling “help” as he goes under for the third time, this is a highly trained professional on what he knows is an extremely dangerous mission that has gone horribly wrong deliberately and repeatedly tapping out “dit dit dit dah dah dah dit dit dit” in order to send it into the void. I suspect most doomed test pilots would spend their transission time at least sending something useful.
Even if the pilot knows he’s doomed, he might still send out a distress signal to let the rest of the world know he’s doomed, if he’s afraid of being made an unperson.