Are there copyrights on fraternity Greek letters?

No, there are no copyrights on fraternity and sorority Greek letters themselves. Greek letters are simply letters of the alphabet, and the alphabet is in the public domain. Anyone can use them.

However, a fraternity or sorority *might* have a trademark on a specific *design* incorporating those letters, or on a specific logo that uses them. This means they could prevent others from using that particular design or logo if it creates confusion in the marketplace (e.g., someone trying to sell merchandise that looks very similar to officially licensed fraternity apparel). But they can't prevent others from simply using the Greek letters themselves in a different design.