An M5M is a Marlboro 5-mile UPC. Marlboro (the cigarette company) has their UPCs marked as 5 miles. These miles are collected to get stuff for free (you need to pay shipping and handling). You can find their catalogs just about anywhere you would find their cigarettes, but most commonly in convenience/liquor stores. You can get free things from t-shirts, hats, and coats to telescopes and pool tables.