The sign there says nothing about 'please respect the monument, do not climb etc etc' which I think is an oversight. It may not stop the most uncaring but it just might stop those who do what they do in a non-malicious, just thoughtless, manner,and of course it gives you something to point to if you challenge anyone about their behaviour.
Is this signboard no longer in situ? It was near the entrance when I visited.(not my photo)
http://www.megalithic.co.uk/modules.php?op=modload&name=a312&file=index&do=showpic&pid=51064
See the Bullet Points top left, third one down.
If the sign's not there now, please let us know.
I know how you feel, once when I visited there was a large American in a red anorak standing on top of one of the entrance stones, braying like a donkey for ages. It was as much as I could do not to impale him on my staff. I had to walk away as I was so cross I couldn't speak to him.
Something is not right. This message is just to keep things from messing up down the road