The Alpha Tau Omega fraternity designates each chapter by greek letters. The first chapter, Alpha, was chartered in Lexington, VA. Since only 24 characters exist in the greek-letter alphabet, as ATO expanded beyond 24 chapters, it cycled through the alphabet again.

The chapter at New Mexico State, Theta Kappa, is about the 202nd original ATO chapter founded. Once a chapter is chartered, it always keeps its greek-letter designation.