LONDON  The advertisement on the bus was fairly mild, just a passage from the Bible and the address of a Christian Web site. But when Ariane Sherine, a comedy writer, looked on the Web site in June, she was startled to learn that she and her nonbelieving friends were headed straight to hell, to “spend all eternity in torment.”

That’s a bit extreme, she thought, as well as hard to prove. “If I wanted to run a bus ad saying ‘Beware  there is a giant lion from London Zoo on the loose!’ or ‘The “bits” in orange juice aren’t orange but plastic  don’t drink them or you’ll die!’ I think I might be asked to show my working and back up my claims,” Ms. Sherine wrote in a commentary on the Web site of The Guardian.

And then she thought, how about putting some atheist messages on the bus, as a corrective to the religious ones?

And so were planted the seeds of the Atheist Bus Campaign, an effort to disseminate a godless message to the greater public. When the organizers announced the effort in October, they said they hoped to raise a modest $8,000 or so.