@Wayne
It might be a bit too subtle, but a partially burnt folder (something mostly whole with a few signed edges and tiny holes) might be fun. . . . But that kind of implies a burnt out topic instead of a hot one. How about a hot pink lipstick kiss? Maybe not. But with the flames, I think that showing the aftermath of the flame is often more effective than the flame itself, but again. . . .
EDIT: Looking at your Buddy Jesus avatar, I'm thinking that a little puffy heart would be just as clear as a little flame--only it conveys that people love the topic instead of it being a hot topic. It's also a more positive symbol. You think? I'm getting dangerously close to criticism here, but that's not my intent. :-)
Trev