The dock at harbor marina at pomme de terre has a sign like that too. I was fishing there during a tournament back in May and they guy came out and gave me all kinds of grief. He threatened to call the water patrol on me. I was pretty sure that he couldn’t say where I could or couldn’t have my boat and where I could or couldn’t fish as long as I wasn’t on his dock, but I was getting ready to leave anyway. So I left.
Later that week I called the water patrol to see what they had to say about it and they confirmed what I already thought I knew. They can control who gets on their dock, but they cannot regulate who fishes around their dock. As long as you are in public waters, you are good.
Call the water patrol to confirm if you wish.