This paper describes a method based on Guided Ultrasonic Waves for the structural health monitoring of sign support structures. The general framework presented in this paper is applied to ultrasonic data collected from an overhead sign structure removed from service, and tested at the University of Pittsburgh under varying environmental conditions. The probing hardware consisted of a National Instruments-PXI platform that controlled the generation and detection of the ultrasonic signals by means of piezoelectric transducers. The effectiveness of the proposed approach to detect damage under large temperature variations and dry/wet/snowy conditions is demonstrated. Finally, the same hardware / algorithm system was applied for the health monitoring of two structures deployed in the Pittsburgh (Pennsylvania) area.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.