"SrA" stands for senior airman, according to Military-Ranks.org. It is the fourth and highest enlisted rank in the U.S. Air Force. Senior airman is the rank just above an airman first class and just below staff sergeant.
A senior airman is promoted from an airman first class after 36 months of service and 20 months as an airman first class or 28 months as an airman first class, along with a commander's recommendation. Some responsibilities of a senior airman include being proficient in technical abilities, developing leadership skills and sometimes supervising lower-ranking airmen. A senior airman is required to study at the Airman Leadership School for six weeks, which is the first part of the Air Force's required professional military education.