I have been returning credit card prepaid application envelopes for years. I save all my other junk mail and "stuff" the prepaid return envelope with the saved junk mail. ( if I run out of junk mail I will use local grocery ads in it's place). Those little bar codes on the back of the prepaid envelopes used for tracking, ect. don't worry. Never heard a thing from any of them. They send me junk, I return the favor!