In reply to Aztec Bar:
I don't think it's as daft an idea as some people are making out - we recently went to Wyndcliffe Quarry, and found that the guidebook mostly says things like "a line of bolts up some nondescript grey rock to the right of the previous line of bolts up some nondescript grey rock". That was normally as good a description of the route as anyone could have come up with, but it wasn't always that helpful, particularly when someone had stuck two extra lines in the gap since the guidebook was written.
It also seems a bit weird to treat it as a basic moral principle to avoid the SENSELESS DEFACEMENT of a PRISTINE NATURAL ENVIRONMENT like, erm, Horseshoe Quarry with SMALL BITS OF PAINT, despite being generally okay with drilling loads of holes in it and hanging bits of metal out of them.
OTOH it is probably still a bad idea in the grand scheme of things even in the places where it'd make sense locally, because you're opening the real possibility that someone with a can of paint and limited intelligence will assume that if it's been done at Horseshoe then it must be a normal thing to do, so it'd be a nice service to the community to do the same thing at Burbage South boulders or something.