No doubt that Shah Rukh Khan has a very dedicated fan base, however pictures came out of graffiti on Shah Rukh Khan's Mannat. Shah Rukh Khan celebrated 23 years of Bollywood by thanking his fans in 23 different ways. His fans decided to return the favour by spray painting on the wall. One may argue that it's a form of mischief, but if you look closely you can see that it says "LUV U SRK." This shows that whoever did this had no malicious intentions, but Shah Rukh's reaction remains unknown.
One could point out that this has a connection to Shah Rukh's upcoming movie Fan in which he plays a characeter who is adores his hero. This may play right along the lines of that film!