Other blogs have talked some more about this, including the
New Humanist blog. The ads follow the format of "Rhetorical question?" and three tick boxes labelled "yes", "no" and "probably".
The one in London reads "Does God exist?" and people have been arrested for defacing the adverts by ticking "No". Many people have complained that two out of the three options are in favour of God existing and there should at least be four options, for example a "probably not" box.
But there is another version that reads "Is this it?" and I laugh every time because the phrasing of this one means that two out of three options are in favour of there not being a God and we can all go about our business.
The power of language.