At the bottom of each post, there is the line that separates your signature from the body of the post. When I view the forums, I get the posters IP address and the 'Report to moderator' link just above that line to the right hand side of the screen.

It is fairly obvious and stands out well, which makes me think it may be a permissions issue that is preventing standard users from using the functionality, although it does seem strange that it would be available to moderators and admins who can deal directly with the offending posts