Have you entered a contest, you know, put your info on a piece of paper and stuff it in a box to win a truck or TV or something? Lots of times this info is sold as well.
Do what I do.
Whenever I enter a contest, or have a subscription, or order something online or through catalog: I change one particular letter(s) in my name and record it in an old binder.
Its interesting to see months/years later when junk mail arrives, I can track it backwards!