Gwern.net:

Some  variables are just plain overused. It seems like no paper is complete without a bunch of E or μ or α variables splattered across it—and they all mean different things in different papers, and that’s when they don’t mean different things in the same paper! In the spirit of offering constructive criticism, might I suggest that, based on  frequency of usage, you experiment with more recherché, even, outré variables?

Instead of reaching for that exhausted π, why not use… ϰ(variant kappa)? (It looks like a Hebrew escapee…) Or how about ς(variant sigma), which is calculated to get your reader’s attention by making them go “ςςς” and exclaim “these letters are Greek to me!”

The top 10 least-used Greek variables on ⁠, rarest to more common: