The Dark Mark

The Dark Mark was known as Lord Voldemort's sign: an ominous skull with a snake's tongue. Lord Voldemort's followers (known as Death Eaters) typically had this symbol branded on to their forearm, like a tattoo. When touched with a wand, the Dark Mark would turn red and create a burning sensation, able to be felt by every other Death Eater in unison, keeping them all constantly connected. The Dark Mark could also be cast into the sky using the spell Morsmordre, signifying a murder had taken place or a heinous attack. A famous usage of this happened during the Quidditch World Cup, when Death Eaters invaded the campsite where the event was held.