Oli Kai Paulus wrote in
:

commercial sightseeing trips on trikes are legal in Germany and are
offered at several airports, e.g.

I guess German aviation regulatory common sense is not quite up to par with
German engineering... shrug

Well, it's technically feasible and and it's legal in Germany. Of
course, the banner size is reduced compared to more powerful
aircrafts.

....and if the banner is smaller, that means the aircraft has to fly lower,
and therefore closer, to the people so they can read it. Hmm. Methinks
there's yet another safety issue here.