Consider the possibility that an unknown person using your name in game is simply working within the limitations imposed by the interface.
If we were standing in a roomful of people and I looked in your eyes, and said, "Your shoe is coming apart." Only one person would look down at his or her own feet. A few others in the room might look down at the subject's feet, too, just out of curiosity. The point is, without saying your name, I can convey immediately which person I'm speaking to here in Meatspace. We don't have this most elementary and primal mode of communication in Planeshift. It takes only a moment to meet someone's eyes, and change your facial expression to something that makes it obvious you're about to speak; it takes much longer to type it in. Because of this, I, for one, use a basic shorthand: The tag identifies each person individually just as if I were meeting your eyes.
Of course I don't know your name; we haven't been introduced. All I have is a "tag" which allows me to look you in the face when I speak to you, in a manner that is obvious to you and to anyone else present.
Using the tag is simply one method for dealing with this particular limitation of the game interface vs. live interaction.