At approximately 13:00 Pacific time, a Let L-23 glider struck a taxiway sign during its landing roll at Arlington Municipal Airport. The instructor and student were not injured. The instructor said the student was just about to land at the north end of the grass landing area when the instructor decided it would be best to land farther down the runway. Without advising the student, the instructor partially retracted the spoilers so the aircraft would float farther before touching down. The glider drifted long, touched down on the wet grass and departed the end of the landing area.