Well when they first started sending them out, they were to be placed over any windows gear you may have owned to cover up the shame. But then as time went on...
Sorry, I can't keep typing with a straight face (even if you can't see it). I'm sitting here laughing at all the things I could have made up.
It's just free advertising. A lot of companies send stickers with the things you buy from them so you can show your "brand loyalty". They expect people will put them on their cars or where ever else you may want to put them. I have a solid black snap on case for my MacBook pro and since you can't see the apple logo anymore, I slapped one on the top of it... And yes, I have one on the back window of my car too.