I don't suppose anyone knows of any way we can try something like this but with a different message/symbol -
http://www.bewareofthegod.com/?cat=9 (http://www.bewareofthegod.com/?cat=9)
Looks fake but is apparently true - http://skeptics.stackexchange.com/questions/7639/is-a-spotlight-like-the-bat-signal-possible (http://skeptics.stackexchange.com/questions/7639/is-a-spotlight-like-the-bat-signal-possible)
I believe certain lasers can project onto clouds, although it might need arranged with air traffic control 1st!