Field-and model-scale experiments were conducted to quantitatively assess the effects of wind loading on Rural Intersection Conflict Warning System (RICWS) highway sign structures. A field-scale RICWS was instrumented with acceleration and linear displacement sensors to monitor unsteady loads, dynamics, and displacement of the sign under various wind events classified by cup and vane wind velocity measurements. To complement the field-scale results, tests on a 1∶18-scale model were conducted under controlled laboratory conditions in the St. Anthony Falls Laboratory towing tank and wind tunnel facilities. Aerodynamic effects on the sign structure were identified through analysis of the mean and oscillating drag and lift forces. Vortices periodically shed by the structure induced forces at a frequency governed by the Strouhal number. The shedding frequency overlapped with the estimated natural frequency during strong wind events, leading to possible resonance. Amplified oscillations were additionally observed when the wind direction was parallel to the structure, possibly due to an aeroelastic instability. The findings highlight the relevance of aerodynamic effects on roadside signs or similar complex planar geometries under unsteady wind loading.