As Richard Dawkins says: “This campaign to put alternative slogans on London buses will make people think - and thinking is anathema to religion.”
I'm inclined to think that thinking is anathema to advertising slogans, inasmuch as they don't allow much room for things like evidence or argument; but insofar as there is a rational motivation for any sort of advertising campaign, it's not to 'make people think' but simply to establish a presence (which is all that advertising campaigns ever really do). And so I would imagine it is here.
Meanwhile, it makes the Methodists happy and got donations from religious thinktanks so I'm sure Dawkins is right that alternative slogans on buses will put religion to flight....