Graffiti wars?

I do hope not, but judging by this message in the underpass I go through cycling to work something may be brewing, which is a great pity.

The grafitti on the underpass walls seems to change regularly and is absolutely stunning - really brightens up a dreary place and, remarkably, seems to deter people from urinating down there. Unfortunately it looks like someone has been defacing some of the artwork.

I really hope it doesn't turn nasty ....