What do the symbols of the Barcelona Metro Mean?

Zafir is right on TMB, which is an umbrella for Barcelona's public transportation network. The inverted C, though, shown in the upper left here: http://www.renfe.es/cercanias/barcelona/mapa_zonas.html, is for Cercanias (Rodalies in Catalan), a local train network that goes to cities near Barcelona and is run by the national rail network Renfe (Though there was talk of Catalunya taking it over). The Catalan train network, FGC (Ferrocarrils de la Generalitat de Catalunya), also intersects with the city network. The symbol is something like 2 stylized chain links, and is shown next to the FGC at certain stops on the diagram above.

TMB stands for "Transports Metropolitans de Barcelona" (Metropolitan Transportation of Barcelona) and includes all transports in the metropolitan area: the subway, the bus, the tram, the funicular, and the Ferrocarrils de la Generalitat, etc. "The inverted C" maybe is the surroundings train service known as Rodalies (Cercanias in spanish) and it's not run by the TMB corporation, it belongs to the Generalitat de Catalunya govt., although you can travel in it, within the metropolitan limits, with a TMB card. http://www.tmb.cat/en_US/home.jsp