What was the purpose of the cereal giveaway Say-No-To-Money Stamper: Kellogg's, 1986

I was just reading the X-entertainment (Something about the writer’s tone turns me off, but I like the pictures of 8os stuff.) article on cereal giveaways , I saw this when I was younger, I had one. What was its purpose? Anyone recall? Somehow, I have seen a million articles there, but this, I can’t get out of my head.