I do not know what your feelings are regarding graffiti, but since Banksy's rise to notoriety, people have really begun to think about graffiti in different terms and graffiti artists have become more and more like social and political poets of the walls. I am not arguing that political graffiti is a relatively new thing, just that the approach has changed. Do a google image search of political or literary graffiti and you will be amazed by the variety, from scrawled messages of "Education for all" to Shepard Fairey's Obama poster, which is an example of graffiti style political propaganda. These images become shorthand for larger issues and ideologies and if they have any power at all, it is perhaps their ability to make us pause and think.
PS. Happy Australia / Invasion Day!