I have also read the
On the Prehistory of Qwerty paper, mentioned in the article. According to it, the first adopters of the typewriter — even before it had been commercialised with Remington — were telegraphists who typed received American Morse code.
The tricolon symbol / vertical ellipsis was by convention used to signify a paragraph break when telegraphing newspaper articles.
One important point mentioned in the original paper was that the the operators' job was to type the articles as fast as the Morse code was received. Even if the American Morse code sequence for a paragraph break was a very long code: eight dashes, advancing the page two lines was apparently considered too slow to do.
The number 0 was sometimes sent as five dashes, and it would only have been at the sixth dash that you would be certain that you got a paragraph break and not a zero, leaving only the time of two dashes to make a paragraph break.
For a newspaper, type-written pages were never supposed to be the final form anyway. The final form was type-set pages. So presentation was not as important as correctness.
I have seen the symbol when writing tables and in mathematics: matrices, to indicate ranges of values/indices.
Here's one example I found quickly by googling:
