How to Spot Unmarked / Undercover Police Cars in Australia
The motorists from Down Under have created a Facebook page where members of the community post pictures of the unmarked patrol vehicles. The vehicles are shown with their plates on, so that they're easy to spot for those who visit the page.
The initiative dates back to July 2011 and while not everybody is spending time on Facebook for such activities, its popularity has grown slowly but steadily. You can check out the Facebook page yourself by following this link.