Legal counter point, I can put up literally any sign on my property. In most states I can put up nearly any sign on public property without permission. See: any flyer stapled to a phone pole or any political sign on a corner.
The actual case here is the fact they tampered with public property without permission by permanently affixing their sign to the pole. Which is at most a fine.
That’s around 140 a week for two people, which is incredibly easy to do if you buy name brand anything. Shits expensive these days.