While I was still living in the suburbs of Washington, DC about ten year ago, I caught a glimpse of what I thought was skywriting in the air above me. I stopped and took out my camera and watched it slowly unfold. At first a circle was formed and I thought that was gong to be it and almost turned away. Then I saw the white returning -- from another direction -- and make a stroke through that circle. Quickly snapping a picture, I watched in amazement as a Null Sign was finished there. No random marks in the sky to be discounted under any circumstance this. I waited for more to be written on the sky, but nothing more happened.
What could possibly be the explanation for such a 'random occurance' like this? I'll never know. But I still have that slide.
We have no way to stop it.