As said, you can usually tell by reading between the lines. If it uses certain words like "restores" "revitalizes" "polishes" "cleans", gets rid of oxidation, etc, etc, then it's a cleaner wax. Usually they don't do very much cleaning at all though - it depends from case to case.
Pro style products (like from Megs) tend to be much more clearly marked.
One thing I like about the Mothers cleaner wax is the simple fact that they're upfront and honest about this. :up Do a search on this product - it seems to be one of the better choices out there. With only a few exceptions though, pretty much ALL the waxes you see on the shelves are technically cleaner waxes. The "Big 3" Mothers, Meguiar's, and Eagle One each make a cleanerless wax sold retail, but that's all as far as I know.