Not a terrible idea. Thread icons can do alot of good, for instance they can describe the type of issue or debate found within a thread, without too big of a title. EX: One icon could be \"Lag\" Inside you could find someone dealing with the common issue of lagging in game, and asking how he could fix his issue. Another example could be a thread icon reading \"Storywriting\" Inside you would find a post with a story.
These aren\'t needed, but they take only 5-10 minutes to make, and help describe a thread to the user without much confusion. We also have to see users take the responsiblility of using the appropriate thread icon, but I\'m sure that wouldn\'t be too much of a problem.