This website seems to be intended to help franchisees create McDonald’s promotional materials.
But it’s quite easy to use it in other ways.
In actuality, I expect that the wording of the banners must be approved by someone before anything is printed. And the fact that the physical banners cost money should prevent this little tool from being misused/abused in the way the Bush-Cheney 2004 Campaign Sloganator was.
(Banner generator link and fake franchisee banner via Adrants.)