erm... as I stated earlier, the site is just outside the village (by a few metres) and already has a wall built into it - do you really think the sign's gonna change anything in terms of ambience?
You made some disparaging remarks in an earlier post about "a few scramblers who can't face real climbing on anything higher than a bus". Shows what little you know about the subject. Scrambling is the stage you find between walking and climbing proper. I know, I do it. You certainly wouldn't 'scramble' a boulder like this - this is proper climbing! The people you'll find bouldering are the same people you'll find climbing the crags further down the valley. Variety is the spice of life, y'know? At the risk of repeating myself, these are (on the whole) a pretty responsible bunch, who self-police very well. A sign would suffice, and really wouldn't affect the site.
Anyway - do you really think ANYTHING is gonna stop an attack with red-paint? Don't forget the Druid's Circle is above Ulverston - a typical small northern town. It has it's share of idiots, the site is extremely accessible... I think you know where I'm coming from. It'd take more effort, and a really good knowledge of rock art sites, to go to Copt Howe with the intent for wilful destruction.