Only works on first and second class mail, and just be unopened. I've been doing this for years and I get maybe 1 credit card offer a month. It's now at the point where most of my mail is actually stuff I want/need and only get mail like twice a week.

You have to write it in red and diagonally as everyone knows.

I wonder if the online services that intend on reducing your email spam would also reduce paper spam.

They work by formally asking all the personal data sharing companies to remove your data