Childlore is folklore passed directly between children, without the input of adults.
https://en.wikipedia.org/wiki/Childlore
Stuff I can think of off the top of my head are paper fortune tellers, summoning Bloody Mary/the candyman, the cool S, parody songs like “Jingle bells Batman Smells” and “Joy to the world, the teacher’s dead” etc.
This stuff has intrigued me since, well since I was a kid. I always wondered where they came from. I never saw adults doing that stuff, so I figured another kid had to have come up with it.
So the cool s has no verified origin ans has occured in childlore functionally spontaneously across every demographic. It occurs in every nation with very little variation, regardless of language, and as far as symbols go, it’s remarkably complex to be appearing so consistently with 14 distinct lines.
For this reason, my silly theory is actually that it’s the yellow sign. The symbol of the eldrich elder god of manipupations of the cthulhu mythos, the king in yellow, Hastur. Thus, among his mind warping eldritch knowledge is the true secret to writing your full name in the cool S font.