Dark Mark

"...You-Know-Who and his followers sent the Dark Mark into the air whenever they killed. The terror it inspired...you have no idea, you’re too young. Just picture coming home and finding the Dark Mark hovering over your house, and knowing what you’re about to find inside... Everyone’s worst fear...the very worst."

- Arthur Weasley

The Dark Mark is the symbol of Lord Voldemort and his Death Eaters. It refers both to a magically induced brand every Death Eater bears on his or her inner left forearm, and to the same symbol conjured in the air by the spell Morsmordre.

Appearance
The Dark Mark appears as a skull with a snake protruding from its mouth. This might have been inspired by the hiding place of the basilisk in the Chamber of Secrets. When summoned, the basilisk would emerge from the mouth of Salazar Slytherin. The serpent is also the symbol of Slytherin house, and thus appropriate to be used by the Heir of Slytherin. The symbol might also be related to the fact that Lord Voldemort was a Parselmouth, a gift he thought made him un-like the rest of the wizarding world. The Dark Mark on the forearm is black, while the Dark Mark conjured by Morsmordre is green.

On the Arm
"The werewolf might be allowed to wear Death Eater robes when they wanted to use him, but only Voldemort's inner circle were branded with the Dark Mark: Greyback had not been granted this highest honour."

- Harry Potter on Fenrir Greyback's lack of a Dark Mark

An inactive Dark Mark appears as a faint mark on the inner part of the left forearm; an active one is jet black.

Lord Voldemort placed the Dark Mark brand on his followers' inner left forearms both as a sign of their loyalty to him and as a method of summoning them to him when he desired. This was done by Voldemort pressing his wand to any Death Eater's Mark, which turns it jet black and delivers a burning sensation to any person with the Dark Mark. Feeling the burn, the Death Eaters then Apparate to Voldemort's side. Death Eaters could also use it to signal Voldemort by pressing on their Dark Marks. Bearing this mark also allows the Death Eaters to bypass a cursed barrier that is also invented by Voldemort. During the height of the Second Wizarding War, they were under orders to only signal Voldemort if they had successfully captured Harry Potter, or face severe penalties. The tattoos faded to scars with the death of the Dark Lord.

Only Voldemort's inner circle were branded with the Dark Mark, which was considered a great honour among his followers. Thus, people like the Snatchers never received one.

After Voldemort was defeated, the dark marks would fade to a scar, similar to Harry's. They would no longer burn, but would remain neverless.

Hermione Granger created special coins for Dumbledore's Army, which would heat up when signaling a meeting, and she claimed that she indeed got the idea from the Dark Mark. However, instead of burning them onto the members' arms, she decided to use coins, something that Harry agreed was better.

In the Sky
As a signature of their work, the Death Eaters can also use a spell to create an image of the Dark Mark in the sky. The incantation of this spell is Morsmordre. The appearance of the one in the sky is basically the same as the one on the forearm, but green in colour. Notable uses include in the woods during the 1994 Quidditch World Cup Final, when it was cast by Barty Crouch Jr., and over the Astronomy Tower of Hogwarts School of Witchcraft and Wizardry by Gibbon in 1997.

Behind the scenes

 * The Dark Mark in the sky and on the Death Eater's arms are different in appearance. The one in the sky is plainly a skull with a snake coming out straight out of it's mouth, while the tattoo branded on Death Eater's arm is much more intricate and detailed, the snake being much longer and winding.
 * The spells used to brand and conjure the Dark Mark were likely invented by Lord Voldemort. He may have based the spell on the Protean Charm, as Hermione Granger mentioned in 1995 that the Dark Mark inspired her to use the Protean Charm to create the method of communication used by Dumbledore's Army.
 * Peter Pettigrew, despite being a low-ranking soldier for his cowardice and lacking skills, is branded with a Dark Mark. However, he is not given the same respect as the other Death Eaters would receive, and is instead treated as a lowly household servant by both his master and his colleagues.
 * In the film versions of Goblet of Fire and Half-Blood Prince, the Death Eaters are seen Apparating out of the Dark Mark's mouth, which is not mentioned in the books. The Dark Mark on the Death Eaters' arms are also jet black, whether active or not. Also unique to the sixth film is that Draco actually shows that he has been branded with the Dark Mark, whereas in the novel, he was only assumed so by Harry, and it was never proven.
 * When Harry mentions that the Dumbledore's Army coin reminds him of the Death Eaters' tattoos, he incorrectly refers to the tattoo as a scar.
 * In Harry Potter and the Half-Blood Prince, the Dark Mark is cast by Gibbon in order to lure Dumbledore to the Astronomy Tower. In the film version, the Mark is cast by Bellatrix Lestrange in celebration after Dumbledore's death.
 * In the fourth film, the skull and snake are green, whilst in the sixth film, the skull is moulded from the clouds. There also seems to be no serpent jutting out of the mouth of the skull.

Notes and references
Marque des Ténèbres Тёмная метка