That is a very good question. If you have travelled around Australia you would be accustomed to seeing brown signs to depict places of interest. The concept of brown signs isn't local to Australia and also adopted in other Countries in the world too.
Australia really has some beautiful places! Through touring Australia, it didn't take long to coin the "brown signs" with the "wonders" and thus wanted to convey this within the logo. The "wonders".
The logo was designed by Kenneth Springer and Ela S. and the goal was to show the winding road as one would see through the travels to the Country side. The "wonders" is depicted with the rising sun, showing mother Earth as the overlay, on top of the brown sign - aka brown sign wonders!