The answer to all this stuff is for the authorities to to act. It is not impossible for these posters to be tracked.
You can do it yourself, but it is a bit technical to do it, and because of the flooding of this stuff, you could never be on top of it.
One way to stop it, is by not giving your primary email address out to any site on the internet, even if you are buying innocent things like clothes.
Just give your email to trusted friends and family. make up a hotmail or other account for buying things etc.
Keep your primary email between you and trusted parties and you will never receive this filth.
You should not have to do it, but it is the World we live in,
Whoever stole the Sun, put it back and we'll drop all the charges!