I was advised by James to take a look at some references of writing on walls in the games Left for Dead and Portal, I also had a look at Assassin's Creed because in this game it is not as obvious and the character needs a certain skill in order to read the symbols and codes.
Left 4 Dead has a lot of bold messages aimed at the good characters with the intention to strike fear into them. They are written on the obvious surfaces as they would appear in real life on walls, blackboards and tunnels.
In Portal the writing seems to be a mass of codes and messages intended to help the character. It is displayed with posters and scibbles designed to fill the space. This could be a good influence for my idea of the message becoming obsessive and understanding the mind the particular character was going through.
Assassin's Creed has hidden codes and symbols that relate to historical culture groups and secrets of a powerful artifact known as a piece of Eden, to the untrained eye this message/code would completely confusing and crazy. The top image is a perfect example with the random numbers and symbols and it might work in my scene to have a message that only made sense to the person who inscribed there.