Having spent all my life in Quebec, flashing green lights have nothing mysterious for me. But that was until I found myself in Vancouver (British Columbia), about to turn left and noticed multiple cars in the opposite direction crossing the street, before I overcame my initial shock and turned, looking in the opposite direction's lights to confirm that they were also green, at the same time. I had visibly missed the primer on British Columbia's traffic code.
Lewin Day’s article on the topic explains my confusion and the meaning of the flashing green in BC. An idea surely intended for safety, but so non-standard it is dangerous. Indeed, a sign which is generally reassuring is―in BC― instead a sign requiring extra caution!