Is it pure fanon that Voldemort can cause pain through the Mark? I mean, we know that they are some method of communication between Tom and the Death Eaters, and we know that the mark he placed on Harry - his scar, which is NOT a Horcrux, I don't care what anyone says - causes Harry pain, but I just realized that I don't remember any canon incident in which we are explicitly given to understand that Voldemort is directly affecting any physical process through the Mark. There's a reasonable canon implication that the Mark might be useful as a tracking device - Karkaroff's body was found in "a shack up north," which was likely a remote hiding place that Voldemort would not have known where to find otherwise - but the pain thing...I'm trying to remember where that came from, and I absolutely don't remember.
Actually, I'm thinking that maybe the pain thing has to be bullshit, because if Tom can cause pain or other physical harm at a distance, he would have used it to kill or incapacitate Death Eaters who had been captured. Yeah? I don't know.
The Lexicon index entry for the Dark Mark crossreferences the Protean Charm (the entry for which mentions that Hermione got the idea for the DA coins from the tattooed Dark Marks), but that's it.
You guys know how much attention I pay to detail; this is driving me nuts.