I wish to put my 2 cents on the status of the "No fishing" sign:
If the road is privately owned, I don't think the private person (or any other person) has any power to order No Fishing, or power to fine his fellow citizen. If he wants people to stop fishing on his property, he can say "It is a condition of entry into this private property that you do not fish." I doubt a private person is able to fine his fellow citizen because his fellow citizen did something (admittedly within his property) that he does not like. Australia as we know it would be a chaotic place if such citizen fine is allowed. Imagine you come into my restaurant and on your way out, I fine you $5 for "eating behaviour which I find very offensive." Would you pay that fine? You probably would, but only if you could stick it into my bodily part which has no benefit of sunshine.
If the road is publicly owned, the only public authority which has the power to order no fishing is probably the fishery (me think). If the water is not within protection or sanctuary zone, I doubt the fishery can find power any where to support its order for no fishing.
We must stand up against this tyranny! THIS IS WAR! Sisters and Brothers, armed yourself with quills, ink and papers. We shall tear this injustice with Words and good sense. Civilisation as we know it lies in your hand.