Pilot Long departed Big Spring, Texas with two passengers VFR to Saginaw Airport, Saginaw, Texas. The pilot was flying to MWL, VOR 065 radial, descending to pattern altitude at Saginaw Airport. The pilot said he had not been to that airport previously. Heavy smoke from a grass fire burnoff was obscuring a large area to the north and east of the Saginaw Airport runway. Pilot Long entered the smoke area, identified what appeared to be a runway and landed. The airplane landed on a street approximately 3/4 mile east of Saginaw Airport and struck a two-inch pipe warning sign resulting in substantial damage to the right wing. There was no fire and no injuries. The ELT was not activated. The FAA investigator was at the takeoff end of the Saginaw Airport at the time of this accident and observed the heavy grass fire smoke obscuring a large area across the approach end to Saginaw Airport and the ILS final approach course to Meacham Field. Pilot Long is blind in his left eye.