I received this tip. If it is true, the police maybe able to help if they're fast enough.
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 number in reverse order. 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.
Lots of thanks to Eyna for helping clear this out all the way from Germany! The tip above is not true. See Eyna's comment for links about this legend.