Or is it money exchange with sign manufacturer? In this case are outdoor signs OK if owner personally made them?
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...
For that matter, would it be prohibited for employees to promote any product in any way?