Two women were targeted in jewellery thefts in Watford and Rickmansworth last week after being approached for directions by strangers.
Last Friday at about 10.15am, a woman in her 60s was stopped by a motorist in St Mary’s Close who asked for directions.
When the woman leant into the car to give directions, a passenger in the rear of the vehicle attempted to give her a necklace to thank her.
Whilst doing so she removed the victim’s necklace and the car drove off.
Later that day at about 11.30am, an 88-year-old woman was stopped by a man in a car in Rickmansworth High Street.
He asked her for directions to the nearest hospital and her necklace was removed.
Hertfordshire Constabulary is warning people to be vigilant.
Detective Sergeant Jo Goodson said: "We believe the car used was a black saloon type vehicle and there were three people inside it, two men and a woman. They are swapping the victims’ jewellery with very poor quality necklaces.
"I would ask people to be aware of this type of crime and the method used. If you are approached in this way, please take down details of the vehicle and contact police immediately via the non-emergency number 101."