Over the past few weeks, a number of incidents have been reported in Leeds, Bradford and Kirklees.
In the majority of cases the suspects have followed the victim in their car and bumped them at low speed with their vehicle. When both cars stop, they tell the victim their brake lights are not working and get them to leave their car to check. While the victim is distracted they steal their handbags and cash from the car and make off.
The victims have all been women in their seventies and eighties with incidents in Coteroyd Drive, Churwell; Croft House Avenue, Morley; Eastfield Crescent, Woodlesford; Kingsway, Bradford; Windsor Court, Morley; Bradford Road, Batley; and Penny Lane, Huddersfield.
Two men, aged 33 and 38, from Leeds, were arrested this week in connection with the investigation and were charged with robbery and theft in relation to two incidents.
It is thought the tactic may still be being used by other offenders.
Detective Inspector Neil Thompson, of Leeds District Crime Team, said: "This is a relatively unusual method for criminals to use to commit robberies and theft. While we don't want to cause unnecessary alarm we do want to make people aware of what has been happening so they can be suitably on their guard.
"We would advise people to be vigilant and exercise caution if they are bumped while out in their car, and to keep their valuables safe and lock their car when they get out to speak to the other driver.
"We are continuing to carry out enquiries into these offences and have made arrests and charged two people but we will be continue to do everything we can to identify anyone involved in using this kind of tactic.
"If anyone has seen anything suspicious in relation to this type of incident or has any information that could assist in identifying those involved, we would ask them to contact us immediately."
Anyone with information is asked to contact Leeds District Crime Team at Elland Road via 101 or call the independent charity Crimestoppers anonymously on 0800 555 111.