The student pilot reported that he was practicing touch-and-go landings and made a normal landing on runway 28L. Witnesses located adjacent to the runway observed the landing, and stated that the airplane landed hard on the right main landing gear. During the landing roll, the pilot raised the flaps, turned the carburetor heat off, and started to increase engine power when the airplane then began to veer to the left. He then applied full engine power in an attempt to get the airplane airborne. The airplane became airborne and the left main landing gear struck a taxiway sign. The pilot then elected to abort the takeoff and he reduced engine power. He further stated that he switched off the master switch and turned off the magnetos. The airplane continued into the adjacent ramp area and struck a parked helicopter.