The student pilot reported that he was practicing touch-and-go landings at Byron Airport on runway 5. The wind was nearly calm. His third approach to the runway, with 30 degrees of wing flaps extended, was normal. The airplane touched down at near its stall speed without incident. After touching down softly, the airplane suddenly veered left. The pilot reported that he attempted to redirect the airplane back toward the runway, but he was not successful. The airplane impacted a taxiway directional sign, and the left wing's lift strut was bent. No mechanical failures or malfunctions were reported by the student pilot during the flight. The Federal Aviation Administration coordinator reported that a subsequent examination of the airplane by the flight school's operator revealed the brakes functioned normally following the accident.