1 I think probably is fine.  Probably simply means more likely than not.  Simply because there is zero evidence of god does not mean it is impossible that there is a god.  I don't believe there is precisely because there is no evidence.  But tomorrow if he knocked on my door and was like, oh I was in the hallway behind the coat rack the whole time, then I'd be wrong.    But there probably is not a god precisely because there is no evidence that there is god.  I don't think probably means there is any evidence of a god.  I just think simply because there is no evidence of god does not mean with 100% certainty there is no god.  It just means there probably is not.

2 But in order to establish ANY likelihood at all (probability) you have to have some -- even the smallest amount -- of evidence to support the claim.  In the case of god, not only is there NO evidence whatsoever, logic alone stands in contradiction to the claim. (Depending on what one means when one utters the word 'god' of course.  Hugh Jackman is a god, for instance, and he's definitely, thankfully, real.)

"Probable," as a description of claims about reality, does not apply to arbitrary claims.  If you assert something, you're obliged to provide evidence for it.  If you provide no evidence for it, there is no way to determine if it is true, false, probable, or even possible! (Possible statements even require some SMIDGE of evidence.)  Put more directly, arbitrary statements are to be ignored.

You are correct that: the lack of evidence does not disprove the existence of god, it only renders the statement arbitrary as no evidence has been presented.  That's IF we assume the skeptical stance on this topic.

I'm not a skeptic, though, so I would cite the entire universe as contradictory evidence for my claim against the existence of any supernatural critters, godly, or otherwise.

3 Here's an example of an arbitrary claim that some may be tempted to categorize as possible instead of just ignoring it:

There is a human being standing on the surface of Mars right now.

There is absolutely no evidence at all to support this claim.

Some people might be tempted to say that the claim is possible since Human Beings and Mars both exist and people have learned to travel in space and land on things they find there, so someone maybe might have sneaked off of Earth and taken up a spot on the red planet. However, the existence of those various aspects of the claim does not provide a link to reality sufficient to support the claim for any evaluation at all.

If someone came to you with a statement like this, the only response you could give apart from just walking away is to say, "What makes you think that?"

Your goal here is to establish whether or not any given claim is true or false.  Some claims, however, lack sufficient evidence to make a determination.  The more evidence there is, the closer you come to saying that a statement is "true."  With only the smallest bit of evidence, you would say that a statement is possible.  With a bit more evidence, you say a claim is probably true.  And when every piece of evidence discovered so far supports a claim, you say that the claim is certainly true.

Claims of certainty are not claims against future evidence because all knowledge is contextual.  Even claims that are certain may turn out one day to be false, but that does not change their status as knowledge within the context of past understanding.

But arbitrary claims cannot be evaluated.  They're just floating nonsense because no one has bothered to try to anchor them to reality.

4 True, but I still say if I said there is probably not a person standing on Mars right now, I'm still correct.  There probably isn't. 

But hey, I guess if anyone is making any such statements on the sides of buses, it is progress.  I can't see that happening here in America. 

5 You're correct only in the colloquial sense of the word. 

Mathematically, since the set of data there is null, there is no probability to calculate. You can't even say there's a 0% probability because that also implies that there is data to consider.  A computer calculating it would just return "null."  And philosophically, the claim is arbitrary and so it's improper to categorize it with other statements of knowledge by discussing its probability.

On the bright side, though, there are atheist bus signs running in DC.  But they weren't as aggressive as the ones in London in my opinion.

6 Sadly I'm sure some disgruntled WMATA bus drivers are behind the wheel of those buses in DC running red lights and acting rude and nasty.    I do not miss DC buses.

7 HA!