Bethesda is re-releasing the old game. It cancelled the old trademark in 2007, most likely because it stopped producing copies of the game which meant it couldn't fulfill the use in commerce requirements to maintain the registration. The second renewal is simply reflective of the fact that this is an intent to use filing and they haven't put the game back into circulation yet. Bethesda may not have any intentions to do so in the foreseeable future ( you can file up to 5 extensions for a total of 36 months to re-introduce the product into the stream of commerce once you get the notice of approval).
If you look at the application date it's March 10, 2011, 8 months before Skyrim was even released. Compare that to Dawnguard which was filed on February 17, 2012, Hearthfire filed on May 24, 2012 and Dragonborn filed on September 25, 2012. It doesn't fit the pattern for the trademark applications for all prior DLC releases and it makes little sense that they would name the DLC after already released content rather than establish a new brand. This is just more wild speculation from fans that are desperate for information on new DLC content.