How to Add icon to a specific category posts

This tutorial should help you: http://wpninjas.com/easily-add-text-to-post-title-based-on-category/

Just change the appended text to an image URL –

function my_modify_title( $title, $id ) {
   if( in_category( '*your category name*', $id ) ) {
      $title = '<img src="*YOUR IMAGE URL HERE*" alt="" /> ' . $title;
   }
   return $title;
}

You can make a little plugin of this so it will work even if you change your theme: http://codex.wordpress.org/Writing_a_Plugin

There might be a better way but that’s the first suggestion I’ve come across.

Good luck!