Possible Clues:

• Greek letter 21
• Greek letter, or the first three letters of a Pennsylvania city
• Symbol of Euler's totient function
• Letter two after tau
• Zeta ___ Beta
• Ancient excerpt from Aristophanes
• Greek character’s exclamation of distaste for listeners
• The Sixers or Eagles, on scoreboards
• It's written as a vertical line bisecting a circle
• The Flyers or 76ers, on scoreboards