Well, I don't think they'd actually know what you look like. Sure, they might have heard the rumors that there's a soul sucking person wandering around Skyrim, but they wouldn't know that you specifically are that person who can call down the wrath of dragons upon their stupid asses or that the Harbinger of the companions is also the guy who killed the Emperor and restored the Thieves guild.
That would be how it would work if the world of Tamriel had any logic, but since guards telepathically know you're a companion or that you're good at alchemy, it all goes out the window.

Nonetheless, there would still be no excuse for attacking someone in full dragon bone armor and riding a demonic shadow horse.