I don't know if it's just me but it seems that when I review, it takes a bit longer to load an audit item as opposed to a real item needing reviewing. Since I noticed that, it's been like that in most cases and it's sort of giving away that it's an audit.
Still, it just makes me extra careful on those long loading ones
If you need to take extra time and care over audit reviews then you're not spending enough time on real reviews.
If anything, arguably, the real reviews (not audit) warrant extra time as they're more important. As whatever action you choose on a real review has an affect on someone's answer, question, mod time, etc, and not just a fake one for a test that the system auto handles.
I've spotted an audit review once or twice, and when (for example) it's a non-answer needing flagging as "not an answer" the only difference for me was I did the audit quicker, because there is no love to potentially give to the non-answer like commenting to try to get the answerer to change it, and so I just quickly click flag.
But whether real or audit, or they take extra time to load or not, I think the point is to not try to ascertain when a review is an audit, or spend different time over one or another, and instead just action all reviews with consistency and accuracy and any you do will be fine.