A Sensible Approach to Graffiti

Conventional graffiti abatement programs advocate immediate and utter removal of all graffiti, arguing that one tag invites others. A clean wall, on the other hand, makes graffiti artists and taggers forget what they were doing and they usually go home.

Portland takes a straight-up, hard-line approach to graffiti. Here is a link to the city of Portland's graffiti policy.
You'll notice its a violation to leave unsolicited markings on your public building, in public view, for more than ten days.
The basic policy is remove all graffiti as soon as it happens so it won't result in 'social deterioration'. Anyone who has tried to wash paint off a wall, especially enamel paints, knows that it can be extremely difficult and takes a lot of elbow grease and some powerful solvents. On the other hand, anyone who has tried to tag a wall knows that it is extremely easy and merely requires a can of spray paint or a paint marker and a few flicks of the wrist.
That said, Portland, and many other cities that employ a similar graffiti abatement program, are fighting a loosing battle. As quickly as they can paint over or scrub off the tags, along comes another eager artist, excited by the prospect of a blank canvas.

Banksy may actually be on to something here. More than just a tongue in cheek invitation to tag the holy hell out of a wall, this image hints at the most likely sustainable solution to graffiti problems.

If we want to find a more effective graffiti abatement program, we need only turn to our northern neighbors, specifically the city of Vancouver, BC.
Rather than focus exclusively on Graffiti removal, Vancouver employs graffiti artists to paint murals, providing the walls, the paints, and a small stipend for the organizers. This may seem counter-intuitive at first, paying the criminals to do there thing, but in fact, it seems to have a profound effect: walls that were once plagued by tagging and graffiti are now decorated with murals.
To understand how this works, consider why taggers are throwing their names up on private property in the first place. They want recognition, and they have a disrespect for the property they are marking. Now, imagine that same wall is covered in a mural done by some of the city's most respected graffiti artists.
Suddenly, the lone tagger in the night is inclined to respect the hard work of their peers (the graffiti artists who painted the mural)and would certainly no longer desire recognition if they were to paint their own initials over the mural. In fact, many would-be taggers would be more persuaded by the threat of expulsion from the graffiti communities than by the legal repercussions should they be caught.

The City of Vancouver, BC graffiti abatement program encourages graffiti artists to organize into registered groups that contract with the city to paint murals in areas with tagging problems.
City of Vancouver Graffiti Abatement Site