The pilot of the tailwheel-equipped airplane reported that the airport had recently been closed but the applicable Notice to Air Missions (NOTAM) had expired, and he flew to the airport. Upon arrival, he overflew the field to check the wind direction and then entered a downwind for the runway. The approach was uneventful until just before touchdown when the airplane struck a steel structure, which was a runway closed sign, that had been placed near the runway threshold. The pilot further reported that he did not see the sign before impact due to visibility limitations of the tailwheel-equipped airplane on approach. The airplane subsequently nosed over and came to rest inverted, resulting in substantial damage to the vertical stabilizer and rudder. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The pilot thought that the NOTAM of the airport closure had expired. It was determined that the airport was meant to be temporarily closed, but the applicable NOTAM was inadvertently allowed to expire and was not renewed. Appropriate mitigations have since been incorporated to prevent recurrence.