A few weeks ago I was driving when I noticed what I think can best be described as Dot Matrix Sky Writing. There were 5 jets cruising along puffing smoke in a coordinated effort to spell out "Geico" across the sky over and over again. The results was pretty neat:
Alt: The word GEICO spelled out with puffs of smoke against a blue sky
I'm not sure if you can make out the jets in this image or not, but they are at the right side finishing up the "O". There was a sixth jet that was trailing behind that who wasn't adding anything to the smoke. I guess he was helping to keep everything in line.
I've only seen this a couple times sense. My guess is it's hella expensive for a very short term effect. The new hotness I've seen a few times is coordinate drones with lights on them at night. That's gotta be a couple orders of magnitudes cheaper.