A couple of great photos showing the unique Underground Map-themed livery on GB Railfreight engine 66721. The left side of the engine shows a portion of the original 1933 H.C. Beck design, while the right side shows the corresponding part of the 2013 Tube map. I believe that this engine  is used to perform maintenance work on sections of the Underground, so the theme is certainly appropriate, as is the engine’s name plaque, seen in the lower image – “Harry Beck”

Source: Michael Thorne/Flickr – top image | bottom image