The More Government tries to control this technology the more creative it will become. This was well known in Europe and I am sure that governments in the United States are not worried about the "environmental Impact" of little lights and their batteries. They are worried about the uncontroled communication with vast numbers of people that would not ordinarily get a message of (fill in the paranoid blank).
Technology to the rescue,... again :)
http://graffitiresearchlab.com/?page_id=19
http://en.wikipedia.org/wiki/Throwies
http://graffitiresearchlab.com/?page_id=6
http://www.makezine.com/blog/archive/2007/02/boston_moonimit.html