During the descent for landing, the airplane's engine lost all power so the pilot switched to the other fuel tank, which contained 15 gallons, and then attempted a restart. When the restart was unsuccessful, the pilot executed a forced landing in a city park. During the landing flare, the airplane's right wing impacted a tall sign post, but the touchdown and roll out were successful. A Federal Avaiation Administration inspector examined the airplane on scene and found that the right tank was empty and the left tank contained 15 gallons. The pilot told the inspector that he failed to use a checklist during the restart attempt and, as a result, forgot to activate the required fuel boost pump after switching tanks. After the airplane was recovered and fuel was placed in the left tank, the engine was successfully run with the fuel selector on the left tank.