I do have a different perspective on what was said from BC. I don't think anyone would dig Caylee up, but I do think feelings run so deep regarding what happened to her, that any gravestone might run the risk of being marked up.
My Mother was cremated, two years ago and wanted to be buried-my father died many years ago and was also cremated but his ashes scattered and she always felt badly that there was nothing permanent to show he was here.
So, we bought a plot for 4 cremations/stones, buried her ashes, and on her stone we put both their names even though we had nothing to bury. I tell this story only because a few months later, when I visited the cemetery, the gravestone was marked up, like some sort of graffiti. I was horrified, went to the office and found this happens, not regularly, but it is not totally unusual.
They have special solutions, depending on what was used to clean the headstones and what type of stone it is. The typical culprits are teenagers, who think it's "cool" and many times it's an initiation or challenge.