Traffic signs are only effective when they are visible and perceptible. Improving traffic safety cannot be achieved without properly applying and maintaining traffic signs. An integrated approach combining GIS-based multi-criteria analysis with risk assessment is proposed to evaluate the physical and operational characteristics of traffic signs and to define a level of intervention reflecting the need/urgency to improve their performance and compliance. The multi-criteria analysis is based on the identification and weighting of physical and operational criteria. One of the criteria, sign visibility, was evaluated through GIS tools. The method was applied in Guimarães, a Portuguese medium-sized city, by analysing the characteristics of 35 regulatory traffic signs. Results show that 51% of the signs analysed have physical and operational problems (level of intervention 2), requiring actions to improve their condition. Besides the compact urban structure, with narrow and non-linear streets, the trees planted on the pavements were identified as the main cause of obstruction. Since the obstructed signs are hardly visible within the braking and stopping distances, road users are exposed to significant accident risk. Removing and maintaining regularly the vegetation and replacing some signs are important actions to improve their physical and operational characteristics. The proposed method can help transportation entities in improving traffic safety.