With a few notable exceptions, most cities around the world dub their underground railways the Metro, and signal to above-ground passersby the presence of subterranean public transportation with a big M. Yet, despite the ubiquity of the letter, no two metro signs look exactly alike. Cities add their own signature flourish to their M's. 

With the help of the blog Metrobits, CityLab put together an infographic of the world’s metro signage, showing the vast diversity of M's across 77 cities. 

All of them look like they're designed to go on a superhero's chest. 

See all 77 of the metro logos at CityLab.