Basically the 'British Humanist Association' is raising money to have buses in London and possibly other british cities to carry the message
"There's probably no God. Now stop worrying and enjoy your life."
Here's my opinion this anyway, i don't like it. It's too direct and it's going to annoy people. religions advertise their religions and their churches, not their beliefs. An appropriate response would be to advertise the British Humanist Association, but nobody would pay attention to that. The only reason they're using this message is as a publicity stunt and it's going to make atheists look like dicks, which isn't really fair.
Basically this

Is not an appropriate or respectable response to messages like this
