Mortar shells landing on concrete create a pattern almost like a floral arrangement. In Sarajevo, after the Bosnian War, the mortar scars in the sidewalks were filled in with red resin. The results are called Sarajevo Roses.
Flickr has a nice map that links to Rose pictures in downtown Sarajevo.
I found out about these from reading a recent set of View From Your Window Contest entries on Andrew Sullivan’s blog.