Six hundred “Am I a trap car?” stickers have been given free to drivers to put in their windscreens, and 20 signs have been put up warning thieves of the presence of trap cars.

The vehicles are parked in areas where opportunist thieves may be operating, and often contain valuables such as satelite navigation system or CDs. Police are aware if someone breaks into a trap car and can track them down.

SmartWater – a DNA-like identification liquid – is also being used in trap cars so that the property can be linked to a specific crime, making it useless to a criminal.

Sergeant Dave Bax said: “Although we are using trap cars to catch thieves, we would rather prevent the crimes in the first place.

“The idea behind the stickers is to make thieves think twice before breaking in.

“Anyone who has been given a free sticker should place it in their window to deter thieves.”

n Anyone who wants a free sticker should call police community support officer Helen Grantham on 0845 456 4564.