7 has... Rush Search, which turns a lot of the cool bonuses into "hope you looked up where this is" because I haven't seen any indications where the special items are.
X marks the spot a lot of the time. Otherwise it's usually just places that look unusual or "stand out", like the Dr Wily portrait in Shade Man's level.
I think criticism of Rush Search is valid enough, but I still like it. I like MM7 in general. It's full of weird, interesting, quirky little secrets.