The Barcelona Metro was inaugurated on December 31, 1924 with 4 stops that today are part of the green line (line 3): Catalunya, Passeig de Gràcia, Diagonal and Fontana and became known as "The Great Metro de Barcelona" whose initials are GMB. Some months later, in 1925, the Liceu Metro stop, in the middle of the Ramblas in Barcelona, was inaugurated.
The logo with the initials GMB can still be seen at the entrance of Liceu metro station, although it's not the original. The historic railings are stored in the warehouses of Transport Metropolitans de Barcelona (TMB), municipal company that currently manages all lines of the Barcelona metro. Current are reproductions adapted to municipal regulations installed during renovation of the station a few years ago.
Notably a curiosity of the Liceu Metro stop: it is the only stop in Barcelona where you can not change the direction once you are down on the platform metro, as there is no connection for pedestrians to get from one place to another. We will have to take the subway to another station and change there the direction or you will have to go out to the street and re-validate a new ticket.