By 1930, Modernism had entered popular culture. With the increasing urbanization of populations, it was beginning to be looked to as the source for ideas to deal with the challenges of the day. As Modernism gained traction in academia, it was developing a self-conscious theory of its own importance. Popular culture, which was not derived from high culture but instead from its own realities (particularly mass production), fueled much Modernist innovation. Modern ideas in art appeared in commercials and logos, the famous London Underground logo being an early example of the need for clear, easily recognizable and memorable visual symbols.