Wow, I remember these.
I think that soviet-era spy activities is the best explanation, if you tuned-in to the Moscow overseas broadcasts they had something of the same nature, attention-grabbing snatches of music, or sequences of xylophone notes, followed by messages of encouragement for possibly imaginary "comrades" in various places. But <ComputerScience>the bandwidth must have been minute</ComputerScience> just enough to say "carry on" or "come home".
I'll go read that poem now... and probably wish I had thought of it first.
...thematically some of the poets tend to be very similar to themselves...