The new adobe advertising has given me a (hopefully good) idea.
There should be a default icon that is shown for all tags used in more than a certain number of questions (maybe 500? 250? Different icons at different ranks?). The idea is that it will make it easier for new users to know when they've made good tag choices. It shouldn't interfere with future tag promotions, because you still just show a different icon for sponsored tags.
Maybe we could even steal something back from one of the clones.