Voices do have a unique signature. The technology do identify it is called Speaker Identification. See for instance http://research.microsoft.com/en-us/projects

Voices do have a unique signature. The technology do identify it is called Speaker Identification. See for instance http://research.microsoft.com/en-us/projects/whisperid http://research.microsoft.com/en-us/projects/whisperid > Each person's voice is different. Some sounds, like "s", sound about the same no matter who says them, but other sounds, like vowels, tend to differ a lot from person to person. We use a special way of representing sound, the cepstrum, that captures lots of information, including the characteristic way you pronounce your vowels. Of course, someone could imitate the way you talk; fortunately, the cepstrum also captures certain fundamental characteristics of voices that are impossible to change. For instance, the length of your vocal tract -- the place where sound is produced in your body -- cannot be changed, and different length vocal tracts tend to produce cepstra with different characteristics. By identifying both the way you talk, and the way your body produces sound, WhisperID can do a great job of figuring out who you are.