Squatting can be defined in different ways and if you ask people they will give you different opinions. In my opinion, if you have a registered domain name and using it properly for your own site then it is fine. However, if you are registering a domain for the purpose of selling it and knowingly that someone else is using a version of the domain for the same purpose then that is definitely squatting (technically speaking though not legally speaking). This may or may not be a trademarked domain name and basically depends upon your intent and how you are using it.
Trademarks become trademarks based on the duration for how long they have been registered and have been in use and also on the basis of thier brand/name recognition. In otherwords, if you haven't used a trademark or if it is not very well recognized then there is no trademark case (usually). So, there are two different issues and registration alone does not mean much. With regards to an LLC, it is just a business entity and has nothing to do with a trademark.
You can register your name trademark - just go to your regional public library and you can get an application and file it with the copyright office or you can mail them and they will send you an application. You can get more information at http://www.loc.gov
By the way, just by registering a trademark you are not fully covered and if someone has time and money they can sue you anyway. In the end it usually comes down to, who has the most money, time and resources to fight it out.
Like I have said before, if you are serious get a lawyer. Also, there are not a lot of lawyers who are well versed with these issues with regrads to the Internet as this is all still very new and decisions are made in the court of law. That is why most of the big companies just start threatening you to see if you hand it to them. There are not many precedents with regards to these type of cases and especially one that involves just a domain name. It's all a game.