taken from http://www.hoax-slayer.com/car-jacking-warning.html
[SIZE="5"]Car-Jacking Scheme Warning - Paper on Rear Window[/SIZE]
Summary:
Email forward warns of a new car-jacking scheme in which paper is placed on the back window of parked cars as a ruse to get a driver to leave his or her vehicle so that the thieves can easily steal it.
Status: [SIZE="7"]False [/SIZE]-Totally unsubstantiated
Example

Submitted, December 2005)
Commentary:
This widely distributed "warning" message claims that brazen car-jackers are placing pieces of paper on the back window of parked cars as a ruse to get drivers to leave their vehicles with the keys still in the ignition and the engine running. According to the message, when a hapless victim exits the vehicle to remove the offending paper obstruction, lurking car-jackers quickly jump in and steal it away.
The warning has spawned a number of versions and has been set in several countries, including the United Kingdom, the United States and Australia. Often, the message claims to originate from an official organization such as a police department, motoring body, or insurance company.
The car-jacking scheme outlined in the email is not implausible. It is possible that criminals could use such a method to steal a car from an unwary victim. However, this degree of plausibility does not mean that such crimes are actually happening. Extensive searches of news, police department and motoring organization websites around the world have offered no confirmation that the car-jacking scheme described is actually occurring. If such car-jackings were really happening in three or more nations, it would be eminently newsworthy. If true, the mainstream media would almost certainly be reporting on such incidents.
The Richland County Sheriff's Department denounces the message as a hoax. The Florissant Police Department also denies that such incidents have been reported in its jurisdiction. Both organizations have been inadvertently associated with versions of the "warning". Urban legends website Snopes.com also classifies the warning message as false.
An English version of the message (shown above) states that such car-jackings are currently occurring in London and claims to originate from a UK based insurance company. However, there is no information about this apparent endorsement of the "warning" email on the insurance company's website. Furthermore, London's Metropolitan Police Service website has no warnings or reports about this method of car-jacking.
A number of credible organizations have published tips for protecting oneself from car-jackers. Tellingly, however, none that I could find mention the "paper on the rear window" ruse as a car-jacking scheme to watch out for.
The fact that virtually identical versions of this warning are set in different parts of the world also strongly indicates that the information in the message is not based on fact. Obviously, from time to time, someone alters an earlier version of the message to suit a local audience by substituting local place names or organizations before forwarding it onward. Thus, they are simply recycling an already dubious warning rather than reporting on events that are actually occurring in the targeted area or country.
Given that there are no credible reports of such crimes occurring in any of the targeted nations, forwarding this email seems counter-productive. Alerting all your friends about a non-existent car-jacking crime wave by emailing them a factually spurious "warning" is unlikely to be at all helpful. In fact, in our already crime-plagued society, perpetrating false warnings just spreads unnecessary fear and alarm. Hoax emails of this nature can also tie up valuable police resources because police personnel have to field numerous enquiries about the status of the messages.
These messages should be deleted rather than forwarded.
peace.