So I'm sure just about everyone knows "The Cool S". It's ubiquitous in school culture and if you haven't drawn it, you probably know someone who has.
The thing is, no one knows where it came from. Everyone has a cool cousin or older sibling that "invented" it, or claim it's from some group or company, but it always turns up to be false. In fact, the oldest known example is in a book cataloging street art published in 1973. From there it's been found on basically every notebook and lunch table the world over and represents a big niche in childlore.
So here's where I go off the deep end... What if this is actually The Yellow Sign?
The yellow sign is never expressly described in the story, with the weird wiggly one being an artist rendition. However, in The King in Yellow, a character draws it freehand to show someone. Which implies it's easy to freehand which the current one isn't. Furthermore, think of the purpose. The yellow sign is intends to spread Hasturs influence secretly. The current one, while undoubtedly cool, is also strange and stands out. If you're wearing it on your person, it stands out. The S doesn't. I'm writing this on break and there's 3 in this room alone. No one cares.
Now take a moment to consider the vector. The best time to indoctrinate someone is young. Why fight to catch the random mad reader when you can net up whole classrooms in a single day and whole schools in a week? No one takes it seriously because it's a children's doodle. A thing we draw absent-minded as we remember our youth.
For all we know, we're all infected and didn't even know.
Along the shore the cloud waves break, The twin suns sink behind the lake, The shadows lengthen In Carcosa.
Strange is the night where black stars rise, And strange moons circle through the skies But stranger still is Lost Carcosa.
Songs that the Hyades shall sing, Where flap the tatters of the King, Must die unheard in Dim Carcosa.
Song of my soul, my voice is dead; Die thou, unsung, as tears unshed Shall dry and die in Lost Carcosa.