In the early 1960s two King's School pupils carried out a survey of the graffiti and mason's marks in the cathedral. Their detailed findings are held in the Canterbury Cathedral Archives (see references below). They found some 80 examples of medieval graffiti. Dating of these is difficult but attempts are possible making use of evidence such as parallels in manuscripts, location, accessibility, and (particularly) costume. The pointed shoe, for example, was common between 1170 and 1400. Their purpose is unclear - they are cut with some skill using a chisel and so cannot be casual scratchings for fun. Some form stylised patterns, but there is no evidence that any were ever over-painted with colour. These markings supplement the 'mason's marks' of which the cathedral has several thousand - for one example see our description of the pulpitum screen.
What to see (two examples):
the 'ghost of Becket' shape appears in black the eastern crypt southern aisle (Image 1) - possibly the remains of an earlier painting, but quite likely the marks left by coal which was once stored here
there are five different graffiti of mounted horseman including this example on the north side of the crypt - it looks unfinished in that the rider has no face, but the detail in harness, saddle girth and reins is striking; it is not easy to recognise (Image 2) but it helps to know what you're looking for (Image 3)
Sources: standard cathedral sources; see also Canterbury Cathedral Chronicle 1967 (article by J Horsfall Turner); King's School magazine Cantuarian (1960) for Image 2; Canterbury Cathedral Archives CCA-AddMs-117