I love coming across old graffiti – it's quite common in churches and cathedrals. Look behind the organ in a typical parish church and you'll find generations of bored kids have left their mark while waiting to start pumping again for the next hymn.
You find yourself muttering about thoughtless vandalism, and then realise that it's dated 1630 or 1842.
What's remarkable to me is that almost all old graffiti has serifs. It seems they are considered as essential a part of the letter as, say the cross bar of the A – not just minor decorative flourishes.
Here's an example from a recent newspaper piece about the discovery of old mine workings: