Literally, Dr. T. J. Eckleburg was an oculist in Queens, NY, according to chapter 2 of the book. The importance to the story is his old advertisement sign that resembled a large pair of round eye-glasses with eyes looking through them. The sign was adjacent to the Wilson's garage and apartment. Of greater significance however, is the figurative purpose of the sign. The sign represents moral judgement. It is located at the juncture where West Egg and East Egg join the mainland in the desolate part of town referred to by Nick as "the valley of ashes". It is the part of town where hopes and dreams went to die and it is the part of town where a great deal of immorality takes place in the story. This is where Tom makes plans with Myrtle to meet in the city to carry on their illicit affair. This is the part of town, too, where Myrtle is killed. The eyes are like the eyes of God, passing judgement on all that goes on there. When Daisy drives to Jay's house to meet with him to carry on their illicit affair, she, too, has to pass by those eyes. A great deal of the story has to do with morality, or the lack of it, and how immorality brought down the American dream. This billboard represents the judgement of all that immorality.