Muggles' Guide to Harry Potter/Magic/Dark Mark

Overview
The Dark Mark is a sigil or sign, being the image of a skull with a snake twisting through it.

Extended Description
The Dark Mark, being Lord Voldemort's sign, is almost as much feared as Voldemort is himself. There is an incantation, Morsmordre, which will create an image of the Dark Mark floating in the sky above the caster; this symbol was routinely left floating above a house in which the inhabitants had been killed by Death Eaters.

Every Death Eater also has a copy of this emblem or sigil burned into his left forearm by Voldemort himself; its clarity and color change with the Dark Lord's power. They also serve as a signalling device; when Voldemort touches the Dark Mark of any Death Eater, all other Dark Marks turn black and painful. This is a signal to all Death Eaters to stop what they are doing and Apparate immediately to Voldemort's side. The communication aspect of the mark also appears reversed, as Death Eaters are able to touch their marks to call Lord Voldemort.

Analysis
It is, of course, significant that the Dark Lord's call involves inflicting pain on his supporters. It is clear by this alone that Voldemort does not lead so much as whip his followers into line; they follow more out of fear and the hopes of getting some of his leavings, rather than out of respect.

It is uncertain how much information is transferred via the Dark Mark. When we first see it used, it seems to be implied that it is acting as a simple caller; Voldemort says that his touching Wormtail's Mark will summon his Death Eaters to his side. Later, we see that individual Death Eaters seem to be able to transfer more information than that to Voldemort, identifying themselves and their locations as well as indicating that they have found "the boy" (Harry). As individual Death Eaters use it to notify Voldemort of events, we also find that it is a broadcast system; at least some Death Eaters can perceive when other Death Eaters report to Voldemort.

Questions

 * 1) Does Voldemort have a Dark Mark?  If so, why doesn't he use it to summon his Death Eaters, instead of Pettigrew's Mark?

Greater Picture
Clearly, when Voldemort summons all his Death Eaters to the graveyard in Harry Potter and the Goblet of Fire, it is then a broadcast, as more than one Death Eater responds. The fact that they responded with such alacrity indicates that they knew it was Voldemort summoning them, which means that the individual touching the Mark, rather than the individual wearing the Mark, is the one identified with the sending. (Recall that it was Pettigrew's Mark that Voldemort touched, not his own – if in fact Voldemort has one.) When Alecto Carrow summons Voldemort because Harry has been located inside Hogwarts, Snape evidently intercepts the message.

Both in the broadcast nature of the communications, and in the ability to pass extra information, one can see great similarity to the Protean charm. Hermione actually notes the resemblance when speaking with members of Dumbledore's Army in Harry Potter and the Order of the Phoenix.