You can completely opt out of the credit card spam ones with a simple sign up on a federal website, but I forget the exact one and am too lazy to hunt it down. Only lasts 5 years though

Or you can do a full mail in thing for the lifetime one, might do that since I just hit my 5 year and started getting spam again

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