Construction signs are often temporary in nature and used to indicate road works, poor roads, or temporary conditions ahead on the road. 

Advance Warning signs include notices of workers and/or machinery on or near the roadway, lane and road closures, etc.  Detour signs are just that--directional signs showing where the detours begin and end.  Road Hazard signs are used to indicate areas where there may be fresh oil, loose gravel or other conditions that might be dangerous for drivers. Supplemental plates are used in addition to other construction signs and can include speed limit notices, arrows, etc.