According to the pilot he was on a short cross-country flight to the Fulton County Airport, Atlanta, Georgia. The flight was uneventful, and he conducted a visual approach to runway 26. The touchdown was normal, however the airplane began to drift to the left during landing roll out. He added right rudder pressure to control the drift, however as the airspeed reduced, the weight shifted from the wings to the landing gear, and directional control became difficult. The airplane drifted off the runway and the left wing struck an airport sign. The pilot exited the airplane and noticed that the left main tire was flat. Examination of the left wing and left main tire by an FAA inspector revealed that the left wing had rib and spar damage. Further examination of the left main tire revealed it was flat, and unable to retain air when filled.