This idea is inspired by the recent news. The papal conclave of 2013 was convened to elect a pope. White smoke was seen emanating from the Sistine Chapel chimney on 13March. The color of smoke has been coded as specific meaning, which known by everybody. Communication can be as simple as that!
As the same time, this idea is inspired by “F-L-O-A-T: kites to gather and display information” posted by Anne-Laure Fayard. I totally agree with four requirements mentioned at the end of her inspiration (/open/usaid-humanity-united/inspiration/f-l-o-a-t)
This submission at least fulfills two of them: “simple technology” and “using the sky as a displayand codes”