IIRC if it's processed as credit, you'll earn the miles, so using it online counts. As long as it's not processed as debit, you're fine, whether or not you physically sign for anything. I would tell you for sure, but I'm not about to count up online and offline purchases in my statements... I use mine online enough that I think I'd notice if the miles weren't awarded.

Interesting about the KeyBank card... what's to stop you from asking for $300 cash back on every purchase you make, then just redepositing it? Does that count towards the amount charged to your debit card and earn you miles?