What it does
For sites that don't have MathJax support, but occasionally need math, HTML codes like
<sup>..</sup> are useful. However, less tech-savvy users may not find this as easily. An example of these sites is Philosophy.
This user script adds a math button to the editor that opens a bar with common mathematical symbols:
Note: I just added the symbols that I thought would be used most, having Philosophy.SE in mind - hence the emphasis on logical symbols. If need be, other symbols could be added (leave an answer/comment here or at the source link above). If you have some symbols that you would like to have, but are not sure others would use as much, you can just edit the source for yourself of course.