Good suggestion, Jeffrey.
I'll add this to my to-do list, as I can definitely see the value in this. The initial implementation will be like the page/post exclusion, where one could enter a string of category/tag IDs. Tags might be a bit tricky, as a single tag could then make the icon not appear on any page/post containing that tag; thinking aloud, it seems that this might cause more trouble than it solves, however, everyone's site is different, and people use tags for different things. I should leave that up to the user to decide.
Fair enough. Consider this on the to-do list, then. I'll leave this thread as unresolved until I have an implementation in place.
Thanks for the suggestion!