While these are example of signs, we surely need to widen what we consider. The Brisbane-centric subjects might include:

Garbage, landfill and wildlife;
Shore birds on, in and above the bay;
Changes to the bay and the effects on birds and people;
Natural processes that shape the Bay
Unnatural processes that shape the Bay ie land fill, pollution, building, creation of the lagoon and the 101 causeway
How to be good neighbors for the birds and the bay (pollution in the bay effects birds)
How people and wildlife can live together.
Where San Bruno Mountain meets the Bay;
Fish in the lagoon and what fishermen are catching at the lagoon inlet/outlet
Seasonal migrations of birds:
Which birds live/visit the lagoon;
History of the Bay - name the peaks and the bays, where did the Native Americans live
Views across the Bay