Just a few people have been making this happen in certain areas of the country and the world. Imagine what we could do if we all got involved.
Addition: The atheist bus campaign is not designed to attack religion, but to let ourselves be known that there are others with no beliefs in the world. We should be able to exercise our freedom of expression and speech just like the religious do over and over again everywhere in our faces. The atheist bus campaign and billboard campaigns simply let other non-believers know that they are not alone, and also lets others who are sitting on the fence between belief and non-belief know that it is okay, they can come out of that closet and will not be alone in the world. It's a simple message and a better one than "Are you going to Hell?"