Is there a easy way to get commonly used symbols without leaving the site?

Question

When writing a question or answer there are some commonly used symbols or typesetting styles that are missing. The two that come to mind are the degree symbol (°) for temperatures and refractometer readings, and subscript (e.g. CO₂) which often come up on the site.

Answer 1

I didn't know this before writing the question - to get the degree symbol, I googled and copy/pasted the symbol from text in the page. There's a much quicker way:

• degree is ° (°)
• subscript is <sub></sub> around the text. E.g. CO<sub>2</sub> makes CO₂