Depending on the nature of your support forum & whether on a hosted plan or self hosted. The Solved #plugin maybe with a custom list of unsolved topics.
There is also #theme-component to help as well. And you can have solved badges earned
There is a new experimental filter with a plugin.
Plugin that can be used with it as well.
This can help with visibility.
If you have #plugin gamification you can have it create custom leaderboards. Publish a weekly leader board or have it show on a page(s) like with right side blocks #theme-component