Wikipedia...In 1946 the Skywriting Corporation found themselves with a fleet of surplus World War II planes and developed "dot matrix skywriting", or sky typing. Skytyping is the process of using five planes in formation to choreograph puffs of smoke being released from each plane. The messages, written at 10,000 foot altitude, can be up to 1,250 feet tall and over five miles long. Traditional skywriting letters are 3,000 feet high and take longer to write.
SkyTypers says it costs $1,500 per message and "variable copy a minimum of 10 times" (not sure what the last phrase means).
So it really doesn't take deep pockets. It wouldn't take much to get a few FReepers together to put up our own sign.
That is a lot cheaper then I thought it would be. Hard to see how they could make a profit.