British TV viewers may have noticed an advertising campaign by UK digital cable channel SKY + that has been running over the last few months, which features a plus sign scorched into a wheat field under mysterious circumstances. After the +'s descent into the field its effect is typical of a UFO landing with various humans looking confused, bewildered and being wrapped in silver blankets as though they are suffering from shock, whilst MIB's and the military - complete with black helicopters - close off the area.   A team of ten people from the production company behind the advert flattened the symbol in a field in Amersham last year. Initially the crop was flattened with boards and they tried to scorch the wheat, however the crop had been dampened by rainfall the night before and so they opted to paint the crop black using emulsion paint!   Ed Van Der Ven from Sky said the + was used in this scenario as a powerful branding symbol, writ large on the landscape to suggest a paranormal force at work. The ad will run on all third party channels for a further few weeks until the next advert in this series is released.     View a mpeg movie of the advert (13.2meg).