This is specifically in regards to parking sign law in Mesa, AZ.
The legal wording is
The owner or the agent of the owner of any private parking area shall be deemed to have given consent to unrestricted parking by the general public in such parking area unless such parking area is posted with signs as prescribed by this Section which are clearly visible and readable from any point within the parking area and at each entrance thereto.
I could not find a clarification of what "at the entrance" means. I can see two interpretations:
Physically situated at the entrance.
Clearly visible and readable from the entrance.