Hey K.,
I've heard that you can turn the diaper around backwards so the tab is in the back. Some kids find that much harder to undo. My son went through that stage of thinking it was funny to take off his diaper...still does sometimes (hes 26 months). Honestly, I don't think it is a potty training sign. Like I said, my son went through that stage big time, but it had nothing to do with the potty for him. He was then and still is - scared to death to pee in the potty.
I absolutely agree with the onesies. That really helped us keep his diaper on. But as far as keeping his hands out of his diaper...good luck. Haha! We gave birth to boys...and they will for the rest of their life have something to explore! HAHA!