I would think that using them as handholes isn't an issue, but that the problem is when the carvings are accidentally used as footholds. Modern climbing shoes have exceptional grips on them that are bound to take a little bit off each time. Even if this little bit is miniscule it all adds up over the years.

The laser scan would have found any that had been 'lost', so I don't think that has happened.

The vast majority of climbers are responsible and should be given credit for it. A sign should be adequate. Climbers will rarely stumble across places like this. Most will have got directions to it from books or the internet. If the books do mention the carvings and stress that they shouldn't be climbed on then that too is probably enough for most climbers.