Although I of course don't condone bullying, I believe changing my avatar to say "ABW" will not do even the slightest to help those that are being bullied. Victims of bullying actually want action taken against their bullies.
So after anti-bullying week is over, what happens? Everyone changes their avatars back to normal? But guess what? Kids that were being bullied before ABW would most likely still be bullied after it as well.