To clarify: You want reports from users about litigable, spam or similar content in the forum messages?

As administrator you can activate the feature to be informed in case of a new posting via email. So you should have an overview whats going on. Additionally there is a link named "spam" for reporting a posting. I don't know if this link is accessible to registered users because I'm a moderator in this forum. If it is accessible to registered users, this is IMHO the proper way for reports.

[edit]In that moment I see that the link "spam" is only implemented for the thread opening message. The link should be accessible for every posting.[/edit]

Yes. I don't want to moderate the site beforehand (time consuming + potential issue with unconsitutional censorship). But then users should be given the best way to report if they feel the content causes a problem to the community or if it might engage liabilities. In this context, a Report button at post level seems perfect.