Graffiti
Now, normally when we’re berated for walking swiftly on, plugged in to our mp3 players and not stopping to examine the world around us, it is the natural world to which we are meant to be paying more attention. And yeah, sure, the natural world is, y’know, kind of alright.
But another thing which we often remain oblivious to is graffiti. Unless, of course, it is a work by a grafitti “artist” such as Banksy, or such an act of utterly mindless destruction that we brand the person who painted it a “delinquent vandal”. And in extreme cases, handcuff schoolgirls for doodling on a desk. Actually, in the UK we don’t have a really “bad graffiti problem”. On the flip side, neither do we have a good “graffiti problem” - elsewhere in the world, you are far more likely to come across stray works of art, in the place of our foot-high tags.
And the motivation behind this act of property interference? Never having engaged in the act myself, of course*, I couldn’t say for sure, but not being completely aware of all the facts of a thing has never stopped me giving my opinion on it in the past, and is not going to stop me from speculating now!
At its most basic, graffiti is often names. Whether simple letters or massive, stylised tags, people want to draw attention to themselves.

“I was here” a tag proclaims. “I am somebody”.” Then there’s the names inside a heart:

A sign of love? Or one lonely person, hoping that what they write will prove self-fulfilling?
In France, there are a lot more pictures than are to be found in Scottish streets, some of them very good.
(Some of them not, but then you can’t win them all! - and even those which are not so wonderful still show the effort involved in making them, eg:)

A showcase for artistic talents, then? An attempt to brighten up a dark place?
And, of course, you also have the politically-motivated slogans. Again, Banksy springs to mind, but there are also other types, such as the stencilled “Free Palestine” that appeared under my local railway bridge:

(I was initially very impressed by the calibre of the neighbourhood neds, but was then disabused of that notion when informed it was done by an organised group.)

Where the grafitti is can also be significant. In Lyon, for example, there is an eight-foot-high plinth with a horse statue on top; on the underbelly was a name. That must have taken so much effort to do; someone was clearly desperate for recognition.
Then, on the flip side of the coin, I suppose there always can be that element of destruction. Whether it be the simple despoiling of a beautiful place or monument, the coarseness of the language used, of the simple hurtfulness of the content, graffit can always be a fast way to provoke a negative reaction.
The sweetest graffiti I’ve ever come across? Would have to be this:

Written outside a Lyonnaise cathedral, on top of a stone wall from which you can see the whole city. It just raises so many questions, and I love the stories that could arise from it. Was it written by one of a pair, as a pledge to stay together and in Lyon forever? Someone who was just overcome by the beauty of the cityscape? A gang threat? Or an old man, showing his love for the city in which he has lived all his life? Clearly, my creative writing muscles are just yearning to be stretched after almost a year since my short stories in English class, but I think I’ll spare you that ;)
*A heart on a Chemistry bench doesn’t count, does it? Actually, I suppose that can be another motivating factor: boredom, and the fact that so many people have done it before you that one addition won’t hurt, and will give the satisfaction of being a rebel.

