The crop circle shows the "Ingress Gaming Logo"!
According to Ianhfrancis, Ingress is Google’s reality game that uses Google Maps and augmented reality to create a game on your phone. Players fighting to control locations around the world.
The back-story of Ingress is that there is an alien race known as Shapers, which are seeding the world with Exotic Matter through the use of Portals around the globe.
The portals are located at various types of locations including works of art, libraries, post offices, places of worship, historic buildings, the Pyramid of Giza and more.
You have to choose a side: The Enlightened, who believe Exotic Matter and the Shapers are for the benefit of mankind and are trying to claim portals to bring more and presumably, the Shapers, to Earth, and the Resistance, who think The Shapers are malicious and are trying to claim portals to stop Exotic Matter from getting here.
London is Ingress central and the city may be the battleground between the game’s two fractions, the Enlightened who believe Aliens are using portals to transcend humanity to a higher state and the Resistance who would rather they asked permission first.
Both sides have the same goal, to claim portals or take portals from the other side. Claiming enough portals and linking them together creates Control Fields, which gives your side points through Mind Units.
Although it's probably a marketing stunt, you may wonder whether it is a sign to a future event or a warning about Google's dominant position in the world, the crop circle/game that reveals Google's secret war to control London.
Video: Matthew Williams made with his Multicopter spectacular aerial photographs of the crop circle.