Same with TV shows and movies I suppose. I think it’s a neat, less missable, alternative to things like graffitied easter eggs.
I can only think of a few examples like Judy from Cyberpunk 2077’s Ghost in the Shell and Radiohead tattoo that says
there was nothing to fear, nothing to doubt
So in this case were they inspired by the Mexican street gang the F13’ers, or by high school stoners? What’s the 13 for?