They should have a number to txt to report guests.
As good an idea this would be, are people whom are not on a contract be willing to text, and waste credit? Or people even be bothered to get their phones out? In quite a few of the queues (mainly Thirteen and Air) the reception is quite bad. It may also be a small problem in answering these, and passing on notifications to staff to clean it up. But it might work if they set up certain guidelines in what content the text must include: such as a brief description of the person so that ride staff can either warn them or kick them out of the park, dependent on how bad the graffiti is.
It always confuses as to why people would graffiti- there are better ways to occupy yourself in a queue. I always find myself playing a game on my phone in long queues that does not require internet or good signal, due to patchy areas in the park.
Some scribbles may be amusing, but all it takes is one and then many others follow suit and you end up with graffiti coating fences like a new type of paint. Perhaps an alternate is to find a material or a type of varnish that the ink will not stay and stick on?
Bag checks will probably cause more faff than they're worth, and may be dropped some months after starting due to complaints etc. and if the park do only search the occasional bags (by picking out at random) they may become accused of discrimination, especially if they only search those people who look as though they will be most likely to graffiti.
The queues that seemed to be most effected by it were Thirteen and Rita, since last year and 2010 Dark Forest was probably the busiest area of the park. So perhaps they can focus some effort more on the busier areas, where rides have the longer queues?