For example, you use a sword, shield, heavy armor and speechcraft often so the game says, "Alright, you're playing as a Knight."
Then later you ditch the shield and speechcraft and start using spells in your free hand. Now the game says, "Alright, you're playing as a Battlemage."
I'm not sure where it would be displayed. Somewhere in the skills menu would make the most sense. It could also be more detailed than just using the classes from past TES games. Maybe you could be recognized as a Paladin if you're a Knight who uses restoration or a Necromancer if you use conjuration to summon skeletons.
Seeing as Bethesda probably won't implement this would you like to see it as a mod? Any other ideas?