Stick-on coupons that don't get scanned

I remember as a cashier I would try to catch them, but honestly, after ringing up so much stuff, you don't even notice the stickers. You just scan away. As a customer, I always tried to remember to take them off. I usually take them off when I put the item in the cart and stick the sticker to my debit/credit card.. I don't usually miss it then.