I'm glad you felt comfortable asking!
Graffiti tags like this are just the name of the person in exaggerated letter forms (the "Mark" up top might be easier for your eyes to pick out).
But this person chose to make their letters bottom heavy and *very* rounded, so immature minds in the room today (including mine) are seeing outlines of penises with hefty testicles, ample backsides, and maybe a pubic mound.
It just shows that you're more refined than the rest of us, TDA!
@MLClark: 😄