exchanged with whom? If it's a small business, it's likely the owner puts the sign out themselves.

Or is it money exchange with sign manufacturer? In this case are outdoor signs OK if owner personally made them?

Most likely you paid someone to make the sign, and someone else to put it up. Even if you made and installed the sign yourself, you paid for the materials.

I am thinking outside blackboard ones, where owners write message in chalk [0] - they don't pay anyone to write the words, nor do they pay anyone to "install" it (= take it out).

I suppose the sign itself must be paid for... but many eateries are using the same signs for menus, so if owner re-purposed one of the menu signs, is there money involved? Or does owner have to dig in garbage bins to find the blackboard for free? What about writing messages straight on the wall? What about printing signs on the printer your own and taping them to the wall?

Now, don't get me wrong, I think it would be an overall improvement if those professionally-made outdoor signs get replaced by artisanal handwritten (or at least handmade) ones, but I don't think that this is what the original idea was about.

[0] https://www.shutterstock.com/image-photo/text-written-on-cha...

Even for a blackboard, what if it is a paid employee that writes on it? Is it required for the owner to write it themselves?

For that matter, would it be prohibited for employees to promote any product in any way?