These colorful pieces of graffiti contain a coded message, and unless you're a geek you won't understand. That's the point: to separate the nerds from the non-nerds.
Painted on various abandoned walls in London, the pictures feature famous British code-masters, like Alan Turing, who led the team that broke the Nazis' enigma machine. Turing is credited as the "godfather of computer science," and much else.
It's not exactly breaking the Third Reich and winning the War two years early, but it's something.