I've met Buzz in person many times and I have to say this does look like his signature. But the inscription worries me a lot - it's highly unusual for Aldrin. I'd avoid if you can; there are tons of other Aldrin items for sale with likelier authenticity.
The sentiment expressed in the inscription is New Testament; in more than 10 years of searching out Aldrin signatures I have never once seen him make a religious reference (although other astronauts routinely do). Also - and it's hard to say for sure looking at the photo - are the signature and inscription done with the same pen? One looks lighter than the other?
in more than 10 years of searching out Aldrin signatures I have never once seen him make a religious reference
At $25-$50 per word, that's more likely due to there being alternatives that collectors prefer to put their money toward. It's not that it's unusual for Buzz to provide--it's that it's unusual for the payer to ask.
although other astronauts routinely do
Without knowing the specifics of what you're referring to, this observation seems to be lumping everything together into the "astronaut signature" category without taking variables into account.
For example, collectors would be more inclined to pay the crew of Apollo 8 for Genesis inscriptions, since that was a pretty iconic part of the mission. As such, you'll probably see those out there (at least from Borman & Lovell).
The comparison to Buzz wouldn't be another religious sentiment, but, rather, something like "Magnificent desolation" or "Contact light" or even "We came in peace for all mankind"--all of which you'll find in decent supply. Like I said above, at $25-$50/word, it's going to be something you really, really want him to write.
On the other side, you have astronauts like Jim Irwin, whose religion was so deeply entrenched in who he was that he'd add those sentiments to many of his autographs automatically--no additional charge whatsoever for them.
In those cases, there's no comparison to Buzz; he's not giving you anything like that for free. His signature pretty much only includes his signature.
To put it simply, you'll find things like that more often from other astronauts because collectors are either more likely to pay them for it or because they're more likely to provide it on their own accord. Buzz, though religious enough to take communion on the moon, doesn't really check off either box for the vast majority of collectors.