Hey Jim,
you are right. I would expect s^2. But there is also a unicode sign “²” (U+00B2) .
s^2 is understood by all programmers. It’s bc language and used this way in most programming languages.
However, discourse forums use the Markdown markup language (including Syntax highlighting in markdown) which supports some html so entering
s<sup>2</sup>
gives s2 
“sub” is also availabe, e.g. for writing things like “CO2”. That’s how I used it to write things like this e.g.:
The downer is, when you copy it, the subs and sups do not remain 
Unfortunately unlike MediaWiki software, the discourse forums don’t support TEX