[spence2]

While this may not be exactly what you need ... I used this hack to add transparent gifs to my posts ... you may want to use "regular" images.

On a per forum basis you assign images to category names.
like...
clear1.gif
Chapter 1
clear2.gif
Chapter 2
etc.

When you enter a thread you can select a category for it. Because I use transparent gifs, nothing shows on the thread ... no clutter.

But on the forum display there is select box with:
Chapter 1
Chapter 2
etc.

If I select Chapter 1, only the threads assigned to Chapter 1 appear.

This doesn't help with search, but it helps to sort your threads.
Your categories could be
Adult Language
Mature Content
etc.

I know it's not the solution you need, but it might get you closer than you are now. Cheers.