Hmm...That would be interesting. I wonder?...
The $LastPostJulian is located at the top of your public_forum_summary.pl file. The "var on_bulb" and "var off_bulb" is where you call the specific images. I think it's possible to add other "var" images for each of your categories.
Looking at the "if" and "else" section of the code you may be able to switch off different images and rename the "on_bulb" and "off_bulb" to something like "on_bulb2" and "off_bulb2".
Where it says:
[/code]maybe you can add the category number something like:
[code]
I'm sure the code is wrong but that may be the general idea. I could be way off the mark however.