Where did that "probably" come from? It doesn't suggest the sales staff is overly confident about its product. If my pilot told me "This flight to Paris probably won't crash," I'd think about taking the train.Indeed, I share the observation that "probably" does detract from the possible maximum impact the ad could've had. The lack of resoluteness, the apparent wishy-washiness of the proclamation all but kills the message. Contrast "There probably are no ghosts" with "There are no ghosts." By including "probably" the statement comes across to believers as "Gee, there's a chance that ghosts exist after all."
Unfortunately, we atheists, skeptics, "reality-based communities" will have to live with this problem. That there probably are no sky daddies is the truth. The reality is--our current state of knowledge is--not that "there is no god" but that those who claim its existence have not provided sufficient persuasive evidence. Were we to drop "probably" we'd have to lay on the table evidence which we simply don't have. Evincing such a universal negative is, needless to say, a tall order. It would've been great to emblazon vehicles with "THERE IS NO GOD!" But that would be a lie. We just don't know with 100% certainty. We don't have enough reasons and evidence to make that leap. And indeed proclaiming "there is no god" would be a leap of faith--belief that is disproportionate to the reasons/evidence at hand.
Were we so audacious as to imply that we are certain of the nonexistence of supernatural beings, religionists would be right in slapping us with one of our own principles of clear thinking: Absence of evidence is not evidence of absence. (Of course the fact that there is a dearth of evidence--for any X--ought to restrain everyone from believing in X, for doing so would be irrational--why believe in X if good reasons for doing so are absent?)
Many ads mislead. I would even say it's the norm. Even preachers, pastors, priests withhold the whole picture and fail to mention to their congregation the epistemic fine print. So we're not going to make the same mistakes as the faith-heads. We are not going to commit the very errors we're exposing and critiquing. We're here to inform and shed light, not distort the picture.
It stands: There probably are no gods.