What do they call them in Mega Man 9 and 10? Those games have achievements, right?
I kind of like stars for Nintendo's own branding, but it would be confusing in Super Mario Universe when you get a star, thus earning a star for collecting 50 stars. But wait, is that the 51st star? No, it's an achievement star. So why isn't it called an achievement? Yeah.
If they have to be different from everyone else, they'll probably go with awards. Nice and neutral, and they can always make the awards look like stars. Maybe that could be part of a customizable scheme, as long as we're dreaming. I'd want mine to look like super mushrooms, fire flowers, and stars for bronze, silver, and gold.