Hi Fleeingfox
From what I understand, the anonymous members are members that decided to stay anonymous. These are members that have signed in, it's just their name that is hidded. You can do this also by modifying your profile.
Also, you can view the forum without being signed in but you can't post anything until you are signed in. I hope this helps.
I am fairly new here but I think that it is a very safe site, not to mention that there are a lot of supportive and caring people here. Just my thoughts.