What do you do when I subscribe?
With the information you provide we will contact over 30 direct marketing organizations and catalog companies and instruct them to remove your name from their distribution lists. This includes almost all credit card applications, coupon mailers, sweepstakes entries, magazine offers, insurance promotions, as well as any catalogs you specify.
Because some direct marketing companies require an original signature on the unsubscribe request, we will send you several pre-stamped, pre-addressed postcards. All you have to do is sign your name and drop them in the mail.
Official site. Via Josh Spear.