This just in! Zenimax filed for a trademark called "DAWNGUARD" and it appears to be an expansion/DLC for Skyrim.
Shacknews: "Dawnguard trademark filed by Zenimax"
Kotaku: "‘Dawnguard’ Trademark Filed, May Point to Skyrim Expansion"
VG247: "Bethesda files Dawnguard trademark, could be for anything"
Nowgamer: "Skyrim DLC: 'Dawnguard' Bethesda Trademark Hints At Elder Scrolls Content"
.. etc. etc. etc.
It's making the rounds on the internet now. This is just like "In-Game Ads Planned for Titan" happening all over again. /sigh
(In case you didn't know, I already broke the Dawnguard news a month ago. And the Titan In-Game ads I revealed 2 months before it made the news.)