Entering your pin in reverse

What do you think of this? Is this true? I have got this email from my friend Cloud.

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's
seldom used because people don't know it exists..