If they're bookmarking your forums, perhaps they've read everything else on the site and found it doesn't change regularly.
I've been a regular member on a site and bookmarked the forums for that reason. I'm sure many of my members do it also but all I do is keep posting links to pages about the site all the time.
If somebody wants to know the latest news on a particular film, I don't tell them. I post a link to the film page in question. Hopefully this makes them explore a little. It's a bit like banging your head against a brick wall sometimes but they get the idea ... eventually.
