Ok so I made some progress when I got home. I think this icon is from the a recent steam update that updated the game to include icons to show for some ACTIVE EFFECTS! This has been bugging me all day and I have been thinking about WTF that icon is, let me tell you what I have tried to figure this out:
I made a new character in a new game, no icon. I used "showracemenu" console command and changed to several races, no icon. I loaded back my main character....you guessed it, icon back. I loaded back my new character, no icon. Back to my main character (who happened to be in Breezehome in Whiterun); I have a mod installed that makes fires hurt. I walked over my cooking fire in breezehome, suddenly a wild fire icon with that same "+" appears in the upper right corner underneath the original icon. I step outta the flames, no more fire icon, back into the flames and the icon appears again. Not only one fire icon but if I stayed in the flames several fire icons appeared...
I took 3 screenshots and stitched them together for you all to see what I am talking about. I'm fairly certain it is an icon for some ACTIVE EFFECT, just not sure which one....yet. Fjolfrin, what active effects do you have?