The circular red-and-blue symbol used to identify London Underground stations is called the roundel.
The design consists of a red disc crossed by a horizontal blue bar, usually carrying a station name. London Transport adopted the basic roundel in the early 20th century, and it became one of the world's most recognisable transport symbols.
Although people often call it a “Tube logo,” the roundel is used across the wider Transport for London system, including buses and some other services. Its proportions, colours and typography have changed slightly over time, but the central visual idea has remained consistent.
The symbol is not the same as the Underground map: the map shows routes geographically schematically, while the roundel identifies stations and transport services. Its simplicity helps passengers recognise entrances quickly in busy streets.