Please see the section I pointed you to.
Trail markers need to match in order to make following the trail easier/possible. Each one makes me feel - oh, I should head there!
There is nothing about a park rules sign that makes me want to visit it.
https://wayfarer.nianticlabs.com/new/criteria/guidelines
Wayspots within Large Areas
Wayspots within large areas like parks, plazas, and fields are eligible as well, even if the larger area itself is a Wayspot.
A trail is a large area that can support multiple Wayspots
https://wayfarer.nianticlabs.com/new/help/wayfarer-faq
Should I consider proximity to nearby Wayspots or Wayspot density when analyzing a nomination?
No. As long as the nomination is not a duplicate of an existing Wayspot, it is eligible to become a Wayspot. Each Niantic app has its own proximity rules to determine whether it will be included in the app.
I will be happy to answer more questions about specific examples. I am not good at blanket questions and answers.