I doubt anyone can trademark two letters unless the letters formed a specific term like DS Auto Supply or DS Real Estate which is why Nintendo doesn't market the "DS" but the "Nintendo DS". In fact, I doubt that any acronyms can be trademarked by themselves. Like "AAA" would be too generic, but "AAA Auto Club" is not. If you read some trademark files, you'll note that for example, Apple Computers, INC. might say something like "Claimant makes no claim to the use of the term "apple" seperate from "computers"." and I would imaging vice versa.
My point basically states that your domain should be fine if it doesn't include the name "Nintendo" in it; especially right next to "DS". I would hate to think that we live in a world where every word we say or write can have some kind of copyright infringement tied to it. It always makes me mad when I think about Donald Trump trying to trademark the phrase "you're fired", but I get a little happier just knowing that somewhere out there, there are courts throwing out crappy cases like that.
Good luck!