Can city “Gold Signboards” enhance sustainable tourism development? Quasi-experimental evidence from National Civilized City selection

City branding strategies have become increasingly prevalent in global competition, yet empirical evidence regarding their actual effects on sustainable tourism development and underlying pathways remains limited. This study examines the impact of National Civilized City designation on sustainable tourism development using panel data from 281 Chinese cities spanning 2002–2022 and employing a staggered difference-in-differences approach. Multiple robustness tests confirm the reliability of the findings. Results demonstrate that obtaining National Civilized City designation significantly enhances urban sustainable tourism development levels. Further analysis reveals that city branding operates through two pathways: enhancing tourism market attractiveness and stimulating tourism entrepreneurial vitality, forming a “dual-wheel drive” mechanism. Specifically, the designation increases tourism arrival rates and the number of newly established tourism enterprises. Moreover, service-oriented cities and highly digitalized cities experience stronger promotional effects. The findings indicate that authentic city brand certifications backed by genuine institutional improvements can advance sustainable tourism development through identifiable pathways, providing empirical insights for urban managers to formulate context-specific branding strategies.