Someone, some boffin at one time invented a bracket you could fasten onto a wooden or metal pole, to hold up signs.
This "inventor" somehow convinced the Department of main roads (DMR) that this bracket was great to hang up signs along NSW roads.
Because the bracket it attached to a pole with one coach bolt, so if that bolt is not tight enough because of gravity, the sign will tilt down.
A sample of (DMR) and (RTA ) old white clearway signs affected by gravity

The Road and Traffic Authority (RTA) also used the same bracket and so does the latest version of this
Government Department, The Road and Maritime Service (RMS)
This invention does not get a mention in this list of great Australian inventions found in this link
https://www.australiangeographic.com.au/topics/history-culture/2010/06/australian-inventions-that-changed-the-world/
Because it doesn't work.