Dark Mark
The sign of a Death Eater in J.K. Rowling's Harry Potter books. It's a skull with a snake coming out of it, pretty much. It's marked permanently on their wrist when they become a Death Eater.
Draco was totally acting like a pimp and showing off his Dark Mark.
Homemade Dark Mark
Draco Malfoy's version of the Dark Mark, as seen in A Very Potter Musical. It is a smiley face with a snake coming out drawn on someone's forearm.
I was bored in social studies today so I drew a Homemade Dark Mark on my arm. I got seven high fives from strangers.