Purportedly, these stickers about you winning prizes/offers/discounts. In reality, McDonald's is simply appealing to the prevalent narcissism in people today, to give people a false/fake sense of being important as an incentive to paste this, and to give them something to show to others ["VIP" is written in large size, and clearly this stupid sticker alone doesn't make anyone a VIP]. Also, McDonald's gets free advertising this way. Never mind the threat to safety that comes from pasting a sticker on the front windshield.
