We've done some banner towing, and there's more to it than meets
the eye. An STC'd tow hook with quick release ($$), special banners
($$), ground crew ($$), and special techniques (Practice and more $$).
We use a 7-foot tall banner (biggest we could get) and it's barely
readable at 1000 feet. Not terribly practical at that altitude. The
drag is enormous, climb is poor and the engine gets plenty hot, with
near full power at 70 mph in a 150 hp Citabria. I had a better time
towing gliders.

Dan