Here's the basic joke.
The deathly hallows are three magical items that are legendary in this wizarding world. The elder wand (the straight line), the philosopher's stone (the circle, also I read the British version of the book so I know it as that), and the invisibility cloak (the triangle).
Now, Luna Lovegood's dad is this crazy hippie who tells Harry about them and draws him that symbol (notice his necklace in the second panel, that's the real thing). I decided that, hey, you could totally make a richard out of that. Why not troll Harry?
