Best method? From what I've read, there are suggestions from wire brush and blowtorch to oven cleaner and water. The graffiti is too far away for a pressure hose. Any other suggestions?
What kind of graffiti is it? if its spray paint I would third the vote for elephant snot. I would avoid any reduction techniques (i.e. wire brush) and save those as a last resort. Magic marker is actually extremely hard to remove but elephant snot can also work on this if its granite, just might take a couple applications. Make sure with the elephant snot you let it sit for a bit before washing it off. On granite, you can LIGHTLY abrade the surface with something like a nylon brush and it shouldn't damage the rock. Often though, over abrading the surface makes it lighter than the rest of the rock leaving a ghost image of what you cleaned off. This can be just as bad as the graffiti if its somewhere obvious.