The Dark Mark

The Dark Mark is the symbol of Voldemort, as he engraves it into all of the Death Eaters skin, and when he is reborn, all the Death Eaters feel pain from the Dark Mark. This Mark was also used in the 4th book to tell the Wizarding World that Voldemort, or Tom Riddle, was back to dominate. The Dark Mark is a picture of a skull with a snake protruding from the mouth of the skull, wraping around and slithering about.