If ads were merely about being informative, they would be boring. But ads want to manipulate, so they have to be flashy and appeal to your emotions.
They pollute your mental headspace, and have no place in a healthy society.
Let's ban billboards. And then let's follow that up with a general purpose ban on paid advertisement.
So, in the case of a billboard, if you are paying a landlord, that's advertising. If you are paying a newspaper to print a specific article, that's also advertising. This means paid press releases are also not allowed. Product placement would fall under this definition too - if a specific car brand is paying you to feature their cars in a movie, that's advertising.
Notably, it's not advertising if no payment is being made. If you are making a movie and you decide to feature a specific car brand - and you aren't getting any kickbacks for it - that's completely allowed.
It's also not advertising if it's first-party. For example, a sign that's advertising a restaurant is allowed if the actual restaurant itself is underneath that sign. And it's also not advertising if Disney is pushing Disney movies and products at Disney World, because Disney owns the full creative rights to Disney World and they aren't being paid by outsiders to adjust the messaging.
This definition can even be robust to grey areas like "what if a car brand makes a movie featuring their cars?" - well, how is that movie being distributed? Are they paying people to distribute the movie, or is it genuinely a good movie that people are distributing on their own? Paying people to distribute the movie is not allowed, but if the movie is good enough that people are distributing it anyway of their own volition, then it's okay!
Overall, the definition is pretty large, and paid promotion is so deeply ingrained into modern society that it's difficult to imagine exactly how much would change if advertising was banned. But, quite a lot would change! Pretty much the entire playbook for all commercial enterprises for "how to tell the world about your thing" would have to be re-written, and new institutions would have to be developed to replace advertising.
But I think society overall would benefit greatly from the change!