I find it hard to believe that someone actually mixes these unless they completely skipped all math classes in school.
When little, my brother used to mix up the words "more" and "less" while speaking. I don't doubt someone could mix up > and <.
At some point I realized it's possible to memorize it visually, since then I never mixed it up again
Anyways, the classic mnemonic for that was simple - for < and > the wide part contains more 'thingies' than the narrow part. They're actually taught before numbers or together with numbers, like [pic of four strawberries] > [pic of three strawberries].