If its trademarked by a big well known company with heavy branded recognition and value. They will come after you and they may even make you pay X amount just to make an example out of you. When people do this, they are labeled as "cybersquatters" whose intent is to reg branded domains and sell it to known companies that already own trademark/rights to the name.
Recently, Carlos Slim, Mexican billionaire won a legal dispute over his name - the person who reg'd it wanted $55 million dollars but lost because Carlos Slim has trademark on his name.
Don't worry about selling this name and/or developing it if it is trademarked. It's better than going to court and having the world labeling you as cybersquatter.