Saeviomagy
Adventurer
Thanks for the feedback folks. Like the idea of mass communication, though the idea of multiple wizards filling the sky with messages over a city (the size of Greyhawk for example) sends shivers down my spine. Brrr...
Well, I imagine that if it became a problem the spell would be heavily restricted by the authorities, like skywriting is in modern society.
In fact, since it's a new spell that has this issue, you could play out the creation of the spell, flurry of random sky-writings and subsequent crackdown as background in your world.