I knew HN stripped symbols pretty arbitrarily, I just checked a few non-letter Unicode blocks (Enclosed Alphanumerics[0], Mathematical Operators[1], Misc Symbols[2]) and checked which one HN strips.

[0] https://en.wikipedia.org/wiki/Enclosed_Alphanumerics

[1] https://en.wikipedia.org/wiki/Mathematical_Operators

[2] https://en.wikipedia.org/wiki/Miscellaneous_Symbols