Vibration due to traffic and wind causes fatigue damage to overhead sign structures mounted on highway bridges. Fatigue damage due to traffic vibration depends on the type and dimensions of the bridge, type of bearings, volume of traffic, location of overhead sign structures, etc. Factors influencing vibration are investigated in this study by carrying out frequency response analyses, with the parameters being the bridge, bridge pier and bearing types, the location of the sign structures and the weight of the electronic information panels. It can be seen that the damage increased after replacing the steel bearings by elastomeric bearings. These factors were verified through frequency response analyses. The results obtained in this study can be applied to the development of measures to prevent fatigue damage in overhead sign structures due to traffic vibration.