There is a bogus email about PIN Reversal doing the rounds (below).

PIN NUMBER REVERSAL (GOOD TO KNOW)
If you should ever be forced by a robber to withdraw money from an ATM machine, you can notify the police by entering your Pin # in reverse. For example if your pin number is 1234 then you would put in 4321.The ATM recognizes that your pin number is backwards from the ATM card you placed in the machine.
The machine will still give you the money you requested, but unknown to the
robber, the police will be immediately dispatched to help you. This information
was recently broadcasted on TV and it states that it is seldom used because
people don't know it exists. Please pass this along to everyone possible.
Australian Federal Police. AFP Web site: http://www.afp.gov.au

Suspicious about the content suggesting people reverse their PIN when confronted by a robber (who can do this under pressure!) and no direct link to either the Australian Federal Police warning or the mentioned TV broadcast, I contacted the Australian Federal Police and asked for legitimacy.

This is their reply:

The AFP is aware of this email. The AFP does not endorse this email.
Regards,
Steph
STEPHANIE CAMILLERI
EXEC. ASSISTANT TO MANAGER,
MARKETING & COMMUNICATIONS CHIEF OF STAFF PORTFOLIO AUSTRALIAN FEDERAL
POLICE
Tel +61(0) 2 62757294 Ext 167294 Fax +61(0) 2 62757058 www.afp.gov.au