Referring to the posts above, the logo is a symbolic meaning of a broken empire. :grad:
However, the question is WHICH empire that might be...
The Imperial Empire was once great and now broken, and uses a similar banner.
The Akaviri Empire was once just as great (war of red diamond, people) and was also broken.
The trailer said "we never thought they were real, or never wanted to believe" (paraphrase). at the end of TES:IV the Empire was out of heirs, was missing one city, but aside from, it was not in that bad a shape.
During all of the TES games we have played, the Akaviri have only been referred to as a past threat, and we never actually encountered them anywhere, leading us to believe them to be a myth or legend of the past.
The trailer is obviously not just saying that there are going to be literal dragons in this game. Its is most likely a metaphor to a force that has been famously linked to dragons. Knowing that, two groups come to mind. The Akaviri and the Imperials.
I doubt that the threat are the Imperials. They would be most likely nursing their wounds after the daedra invasion, and not going on a region conquering spree (Perhaps in the time of Uriel, but not now).
However, we have known that Tamriel is absolutely irresistible to the Akaviri (due to their multiple invasions).
Because of these reasons, I believe that an Akaviri attack is much more likely than an Imperial attack.