This is an example of what I call 'architectural graffiti'.

This particular piece can be found within the Chatham Historic Dockyard and was probably executed during the latter half of the nineteenth century. John Shirley was taking a bit of a risk by 'defacing a building in one of Her Majesty's Dockyards' .

You may see this one on the wall of the ropery. Warning, the ropery is a quarter of a mile long ... happy hunting!