On August 2, 1998, at 1330 central daylight time (cdt), a Piper PA-28-140, N8398R, piloted by student pilot, was substantially damaged when its left main landing gear collided with an airport runway marking sign during a takeoff from a touch and go landing maneuver on runway 02 (4,395' X 60' dry asphalt) at the LaPorte Municipal Airport, LaPorte, Indiana. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 instructional flight was not operating on a flight plan. The pilot reported no injuries. The flight departed LaPorte, Indiana, at 1330 cdt. According to the pilot, he was making a third landing on the runway. He said the airplane was "...about 1 to 2-feet off the ground... [when he] noticed..." a pretty strong crosswind over my right wing. He said a "...strong gust of wind blew [the airplane] to the left of the runway." The airplane s left main landing gear collided with the runway marking sign shortly after the airplane's ground track went beyond the runway's left edge and the pilot had applied full power. The landing gear assembly separated from the main spar attach point and fell to the ground during the airplane's climb out. The pilot flew the airplane for about 1-hour before returning to the airport and landing on runway 02.