Ceduna is a town in Australia.
Hitching West towards Western Australia
You would think the BP at the western end of town is a good spot to hitch out. Unfortunately there are plenty of signs around saying "Hitchiking prohibited", also management isn't too keen on strangers asking around. Many people are locals anyway who won't go further west. It's not recommended to wait there
If you walk west towards the intersection of Denial Bay Rd there is a section of about 300 meter, where cars have to slow down to 40km/h. This may be the right spot to hitch a ride, but there are some sort of officers in the opposite who check on incoming cars. So it's probably not a great spot to catch a ride either. As well, most cars turn left anyway at the intersection or are scared to stop in front of those officers.
The best spot is probably when you continue walking past the intersection and wait where the big traffic sign is. Cars will drive very slowly through the slow section and have plenty of time to judge on you. However, there is very few traffic, probably one car every 3 minutes (depending on season) so expect longer waiting times. On the sign are about ten notes from other hitchhikers, so it is certainly a good spot (unless you imagine them waiting for long times to get bored enough to leave a note).
The next bigger town is Eucla. If you use a sign, it should probably say this or W.A., rather than Perth. A ride to Perth will take 3-4 days and some people may not want to give a lift for the whole distance.