I follow Think Atheist on twitter and last night I saw the tweet about the Atheist billboard in Houston....well I had to go find it since I live in the surrounding area. It was a wee bit of a scavenger hunt but my husband and I finally located it above a liquor store on FM1960.
@Tricia: I hope you understand *why* they used the term 'probably.' The first time I saw the word "probably," it gave me pause too. But the point they are trying to make is that science is based on evidence. The strict confines of evidence-based science does not 'allow' us to claim definitively that something doesn't exist (let alone a god) - the best we can do is to say that no evidence yet exists to support it; hence the term 'probably.'
Now, in everyday conversation, when it is perceived that there is ample opportunity for evidence to exist (but it still doesn't), we will just short-hand the whole concept by simply asserting that it doesn't exist at all. Please acknowledge that the effort being made on the London buses is an attempt to stay faithful to the strict confines of science in the formation of conclusions.