I have personally used \varsigma in one of my papers, where I had two different things that needed short and memorable glyphs and both started with "s". \varsig

I have personally used \varsigma in one of my papers, where I had two different things that needed short and memorable glyphs and both started with "s". \varsigma turned out to be surprisingly different enough both from \sigma and s, but I would just give up an urge to make everything a single letter if I were rewriting that paper today.