Banners dissuading posting CP?

For sites which cater to fictional content and allow user generated content to be uploaded, they could have prominent banners on the registration page, and upload forms reminding users not to post CP.

This is very rare occurence and never happens in the way you would expect, however it is important to iterate a zero tolerance policy for this content, to dissuade someone from posting it entirely. The same may apply to legal imagery. Administrators may not want this present in a sexualized environment.