I have just stumbled across this post and became curious about the same question, namely the part regarding the origin/history of the vertical bar symbol $a\vert b$ that we use to denote "a divides b" (I don't care at all about why it is written "backward" in the sense asked there).
While the OP of that post seems satisfied with the answer, the part about the origin of this symbol was still left out. In one of the comments there, there was a suggestion that the answer could be found in Florian Cajori's book A History of Mathematical Notations. I have a copy of that book but I found nothing directly related to the history of the symbol $\vert$ , unfortunately.
I'd highly appreciate if anyone could point me to a good resource about this subject matter, be it a book or an article. More specifically, I want to know the time period the notation $\vert$ was introduced and the names of the mathematicians associated with its development.