Per the developer at that forum thread:

"To be safe, always check the digital signature of EXEs you downloaded, before you run them. The official Classic Shell installer has a signature for "Ivaylo Beltchev", and the fake one doesn't even have a signature."

And per another user (silmar), my sentiments:

"The problem with signed installers is: many software developers don't sign, so you install even if Windows warns you. Even if someone signs and then stops signing, it may be that he forgot about it. But you want to install NOW, so you skip the warning."

Admittedly the download page doesn't mention signing or how to look for that, though, per the comment I referenced above, I doubt it would make much difference to the vast majority of users.