Just because you don't know who, does not mean there isn't a who. There might be far more efficient ways...but maybe they are not communicating over long distances, maybe they are communicating with other UFOs. They have cloaking devices and have been picked up on heat sensors on military aircraft yet not on the official Army radars.
There are very distinct differences between fake and real crop circles. The fake ones might be made by a barrel, string and plank of wood but the real ones are complex in nature . For a start the real ones have radiation readings a plank of wood can't produce. Looking closer the way the wheat is platted, knotted weaved, inter twined and cut is far too intricate for a bunch of hoaxers....you couldn't produce anything like a real crop circle with a plank of wood, at night and within one single night. Legitimate crop circles appear over night.