Huston Metro

This is not actually a subway sign, but a bus stop. Huston Metro (the transit authority for Harris County, Texas) also operates a light rail system.

Photo by hyku. License CC-BY

Berliner S-Bahn

Photo by waffler. License: CC-BY

Kharkov in sunset

Photo by L-plate big cheese. License: CC-BY

Berlin U-Bahn

Photo by J-Cornelius. License: CC-BY-SA

Bucharest North Station

One of the many entries to one of Bucharest's main metro stations: Gara de Nord (North Station). You can see both the old sign (the M on the post) and the new one (above the billboard), as well as the other sign above the entrance, which shows the lines you can use from here.

Photo by rjw1. License: CC-BY-SA

Mosaic

A somewhat neglected mosaic in the Madrid Subway.

Photo by Richard Winchell. License: CC-BY-ND

Newcastle in black and white

Photos by ThunderChild5. License: CC-BY