weed /wēd/ noun, a wild plant growing where it is not wanted and in competition with cultivated plants.
graffiti /ɡrəˈfēdē/ noun, writing or drawings scribbled, scratched, or sprayed illicitly on a wall or other surface in a public place.
street art unofficial and independent visual art created in public locations for public visibility.
Artist David Zinn uses weeds in his graffiti illustrations
British Artist Slinkachu creates tiny people and places them in urban scenes.
Michael Pederson "Urban Weed Awards"
Artist Jan Vormann uses LEGO bricks to patch holes in urban architecture