John Welch and Claire Foley, “Gammadia on Early Jewish and Christian.”  BYU Studies 36:3 (1996-97): 253-60.

• (Gammadia is an anglicized plural of gamma, the third letter of the Greek alphabet. Gamma looks like a 90 degree triangle with the hypotenuse removed, and the corner at the top left, one leg going down and one to the right.
• Gospelink (subscription required). Gammadia section is near the bottom of link. BYU Library Viewer. Free PDF from BYU Studies.