Imageability is a cognitive measure of environmental differentiation and place memory. However, the existing literature focuses mainly on static morphological descriptions or subjective perception, without systematic quantitative studies of how physical environment and behavioral activity jointly generate the imageability of characteristic districts. This limits active responses to the rise of “placelessness” in numerous cities. Based on the S-O-R theory, this study proposes a “visual–activity” two-channel mediation model. Based on 65 typical characteristic districts in Wuhan, and using multi-source data in the research, PLS-SEM was employed to systematically study the process that influences imageability in urban environments. It was found that (1) behavioral activity serves as the core mediating link between the physical environment and imageability; (2) scenic beauty exerts a partial mediating effect between visual sensitivity and imageability; (3) vitality exerts a full mediating effect between activity support and imageability. This study is expected to provide a scientific foundation for design refinements, quality enhancement, and place identity construction in urban characteristic districts oriented toward perceptual experience in the post-industrial era.