It's a graphic that Nestlé is going to place on their candy packaging telling consumers what a serving is and they're literally calling it a "Portion Device" and describing it as "new" and "innovative".
As to my question of whether or not it's the stupidest front-of-package program ever devised the answer to that question is likely the same as the answer to this question - will people still eat the whole package of Smarties (for you Americans they're the same thing as M&Ms) if the front of the box says a serving is only 15 of them (meaning there are 3.7333333 "Portion Device" servings in a 50g box)?
If you're going to put anything other than a warning on the front of a package of Smarties, it should be the calories and added sugar you'd get from consuming the entire box, because that's what consumers do, and no doubt Nestlé already knows that.
(and if you were wondering, the whole box (and not the King size, just the regular) contains 230 calories and 9.25 teaspoons of sugar)