A detailed understanding of the wind forces on large highway signs is crucial for the safe and economical design of the supporting truss structures. Large dynamic message signs (DMS) are increasingly employed to manage highway traffic flow and to provide accurate, timely information to highway users. Recent field inspection data indicates that truss structures supporting DMS signs may be subject to more complex and extreme wind loads that are not accounted for in current code driven design procedures and are resulting in increasing maintenance and fatigue problems in relatively new sign installations. Interim results of a multi-institution 24 month analytical and field monitoring study to better understand the response and critical design characteristics of these new sign structures are present in this paper.