Appearing as part of a series of patterns in crop fields in 2008, we have what seems to depict a blueprint or a device of some kind. It has also been suggested this could depict the solar system planets and a cosmic event or some kind of diagram.
Others have theorised that this is instead some kind of 2D representation of a 3D object that if constructed could be used as an anti gravity device. SPOILER: while it is known that at least 1 attempt at creating the device failed, it is unknown if they were eventually successful or if it let to any substantive outcome.
Interestingly there were several other signals appearing to depict machine parts in 2008, see below.
