Several backlit advertising panels hang from the wall of the Barceloneta metro station platform. Most are vertical and advertise the latest series to arrive on the platforms. There's also a larger, horizontal one, currently displaying a campaign for a children's NGO. Every now and then, a worker comes by to change the posters, but one thing always remains: the name JCDecaux. The more observant will have noticed it printed in small, gray letters along the top of the panels.