Of the many misconceptions that atheists face about immorality, there's always this tendency to demand things of atheists.
The first thing to be demanded is that we prove that god doesn't exist. That's what I like about this campaign. It is clearly labelled the atheist bus campaign, and yet the statement is, "There's probably no god". This accurately describes the atheist position which is that we see no reason to believe in any gods. It's not that we positively declare "There are no gods". It's that we disbelieve the declarations of religious people that there is a god.
Then comes this bit from a minister. Sadly, the writer of the article paraphrased it rather than quoting, but I think the general gist of it is quite common.
The moderator of the United Church of Canada, Right Rev. David Giuliano, said he would rather see atheists say what they believe in, rather than what they are against.
The whole point of atheism is the not-believing, not the believing.
But if you really want to know what atheism means to most of us, I can take a vague guess with which most of us would probably agree.
It means freedom. Freedom from dogma and guilt and everything else religion brings us. But a youtube video already says it better than I could, so here ya go.