Letter origins, yay!
Back when S was first written in the Latin alphabet, it used to look more like a lightning bolt, with really hard edges. As I’ve mentioned in previous alphabet posts, Latin took its letter symbols from Etruscan, where it was written in the opposite direction. Because…it was fun? Let’s go with that.
The Etruscans took their alphabet symbols from the Greeks. You might think that’s weird since the Greek sigma capital is Σ and the small letter is σ. Doesn’t get much farther from S than that! But you should know that there’s more than just one Greek alphabet. The Euboan Greeks, the one that gave the alphabet to the Etruscans, had a partial lightning bolt for S, but other Greek cities used a sideways M that looks a lot more like the sigma it evolved into. Don’t ask me about the small sigma, though. That answer’s just going to be “for fun” again.
Going further back, there was Phoenician. They actually had more than one S, using samekh, tsade, and sin (shin), and it seems our S came from the latter, which meant tooth and looked like a lying down lightning bolt that looked a lot like a W. So S looked like a lot of other letters before it was S, although I guess the jagged edges do kind of look like teeth. Even earlier, in proto Sinaitic, it looked like a rounded W, which apparently meant bow. But I haven’t been able to find confirmation on that, so for all I know it means butt. Which would be hilarious. And now nothing will ever be as funny as that bit of fakeness.