there is a habit in london of bricking up doorways with breeze blocks.
and then doing some nice big graffiti over it (thus ruining the nice
breeze block patter - but there you go - you can't have art without
destroying art I always say)

here is an example featuring an alien:

you can't quite see on the small version, but someone has drawn a
little eye and nose, and converted the mouth to a moustache: