It kind of is since a lot of it grew organically. Often it isn't even consistent across authors/countries. It wasn't really "designed".

The German Wikipedia has a decent overview of symbols and I often use it as a cheat-sheet for LaTeX, whereas the English equivalent of that article has a better explanation of basic notation.

https://en.wikipedia.org/wiki/Glossary_of_mathematical_symbo...

https://de.wikipedia.org/wiki/Liste_mathematischer_Symbole?o...

Even If you don't speak German, the article might be useful because you can follow the links to the individual articles next to the symbols, then change the language back to English. Or use it as a LaTeX reference if you're like me and have trouble remembering some of the more wonky abbreviations it uses. Of course that article isn't comprehensive, but most of the stuff that is missing is very domain-specific.