The graffiti scratched onto the walls of the eastern end of the cathedral are numerous. They vary in size and form, but almost all contain initials or names of the artist.
One of the best names to search for is John Forster, who rather enjoyed scratching his name in the walls. His letter form is rather impressive and he has had enough time to fully form his name and date it. We can assume that he enjoyed making his mark because his name appears twice on the wall of the New Building.
His first signature (should that be graffiti tag?!) was scratched at the north east end of the cathedral. It is dated 1687. Further east on the same wall you can find his second attempt from 1688. Rather pleasingly it is easy to see an improvement in his letter formation and a more confident signature. He used an I in place of J for John because the letter J hadn't come into use yet.
John Forster was likely to have been a pupil of King's School, which was based in the cathedral grounds at that time. How he managed to find the time to mark his name in such detail, we will never know. We can only guess what his punishment would have been if he was caught doing it.