Notification mediums on stations
There are for example stair steps, surfaces on pillars, illuminated boxes betweens tracks and more. It might sound confusing at first but it works in practice. Any station has its own architecture and therefor its own advertising opportunities. This makes a allocation plan sensible which is used to choose your notification mediums. Every station has stairs to the intermediate section and to the streets. For these only the format can differ. Any station has folding monotube frames as well in the formats DIN A0 or DIN A00. Only the locations vary.
The advertising periods are long term for 12 months at least which is positve for the prices. One billboard that is protected in a DIN A0 frame costs only € 80,00 per month.
Local companies use notification mediums targeted on close stations to call attention to their business. The local customers are subtly reminded several times a week of your presence.