This is an interesting one as not only do you find these things underground but above to. I have a leaning towards Calligraphy and have noticed that alot of old graffiti, art (call it what you will) uses type faces often contempory to the era and as such forms a fabulous record of peoples adoption of different writing and drawing styles. I have often noticed in places where people worked anbd rested interesting scrawls and have seen them in various mines, workplaces and places with great views like black rocks. People obviously sat and in their break times or whatever with little to do just scratched away...
Sadly now buried I found a wonderful scratched picture of a sailing ship in a sandstone quarry near Ashburton, superb artistry and dated 1700 T.Byre in Full Old English... sadly the hillside is landscaped and i simply did not think to take a pic...
Another iinteresting factor is it shows that often the people that many seem to think of as witless uneducated wage slaves were artistic and occasionally well educated workman...
I believe a book is due out on all aspects of old graffiti soon (it may be out in fact). It doesn't cover spraycan its aimed at carvings, scratchings etc.
Aaaaaaaaaaaaaaaaaaagh Creeper!!!!!