Control panel > Style & Colors > Forums Icons (under Custom Icons)
Main Forum Listing Forum with new messages Forum with no new messages Topics Listing (forum clicked on) Add New Topic Button Image Mark All Topics Read Button Image Topic that is New Topic that has New Replies Topic that has no New Replies Topic that is Hot (Active) Topic that is Hot with New Replies Topic that is Sticky Topic that is Sticky with New Replies Topic that is both Sticky and Hot Topic that is Locked Topic that is Locked with New Replies Topic that is both Locked and Hot Post Listing (topic has been clicked) Delete Message Button Image Go to Top Button Image Go to Bottom Button Image Reply to Post Button Image Reply and Quote Button Image Edit Post Button Image Poster Rank Images (displayed under poster's names) Rank 1 Poster Rank 2 Poster Rank 3 Poster Rank 4 Poster Rank 5 Poster