You'll find that there is a rather severe performance penalty due to
the increased drag caused by the banner...
[...]
It's a cute thought, and might even make the newspapers/TV news, but
it's a mite impractical, IMHO.

For a small enough banner this might be a minor issue. How small can
your banner be and still be worth doing (for your purposes?)

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.