headache bar
n.— «The state is also considering the installation of a “headache bar.” That is a device that would use chains hanging from an overhead sign near the bridge to warn a trucker that his vehicle is too tall for the clearance. “Trucks would strike the chains before the bridge.”» —“Salina Residents Voice Opposition to Route 370 Changes” by Matthew Cox Post-Standard Jan. 28, 1988. (source: Double-Tongued Dictionary)