One of the plaques set into the wall.

This quote from Sir Walter Scott reads:

When we had a king and a chancellor and parliament-men o our ain, we could aye peeble them wi' stanes when they werena gude bairns. But naebody's nails can reach the length o Lunnon.

(When we had a king and a chancellor and parliament-men of our own, we could always throw stones at them when they weren't good children. But nobody's nails can reach as far as of London.)