An on-board signage system includes one or more vehicles, a display device installed in each of the vehicles, and a signage controller, in which the signage controller is configured to function as a post collecting unit that collects a post content item uploaded to an SNS site, a post analyzing unit which extracts a location relating to the post content item as a relevant location, a post database that stores post-related information obtained from the post content item in association with the relevant location, and a selector that selects at least one of a travel route of the vehicle and an image to be assigned to the vehicle, based on information stored in the post database, and transmits the selected travel route or image to the vehicle.