Residents of several roads in Portishead, Bristol, have reported finding the stones in recent weeks, and believe that they may have been left by a man delivering bags for charity donations.
He's described as white, slim and tall with receding long brown hair and a goatee beard. He was wearing a red T-shirt and driving a 'slightly scruffy' white Mercedes Sprinter van.
And Nick Gough, the area co-ordinator for Portishead's Neighbourhood Watch, says residents should alert the police if they have any concerns.
"There are reports of a male leaving white stones outside of various properties. These distinctive stones are believed to have been left outside of properties which look unoccupied," he tells the Bristol Post.
"If you have received these leaflets/charity bags and/or you have found white stones outside of your property or by your vehicle please contact 101 and let the police know. Tell the operator to tag your call as 'Portishead NHW intel."
In the past, tramps used to leave chalk marks outside homes to indicate, for example, houses where they were likely to be given a meal or little cash - and burglars are believed to have picked up on the technique to highlight homes that could be vulnerable.
So what are the signs to look out for - and what do they mean?
Stones under the wheel of a car are believed to be a way of checking whether it's been moved - which could indicate whether the home is actually occupied or not. If this is the case, then simply moving them could put the burglars off.
A chalked cross
According to police in Torbay, Devon, this mark indicates that a home is a good target. You could always just wipe it away - or, if you want to be clever, draw a circle around it, as this is believed to be a sign that there's nothing worth stealing.
Two overlapping squares is believed to mean that the inhabitant is nervous or afraid. Meanwhile, a mark that looks like an open book indicates a vulnerable female.
Five circles or ovals in the shape of a flower is believed to mean that a home is wealthy.
The letter 'D'
A mark like a letter D - sometimes with a dot or line inside - is believed to mean that a property is too risky to burgle. If you find one of these, you may want to consider leaving it there...
Top 10 burglary hotspots
Top 10 burglary hotspots
Ed Miliband is pictured in Ilford, on the outskirts of this troubled area.
Burglary is a top policing priority for IG3 - which also has related issues with drug use and anti-social behaviour.
Opportunistic crime has been identified as a particular threat, and police are hoping to reduce the number of offences largely by getting people to improve security and reduce the number of opportunities.
Cockfosters has changed a bit since this 1950s photo. Nowadays burglary is such a problem that local police have made this their top priority .
They are aware that a number of known offenders continue to operate in the area, and that opportunistic crime is rife. As a result they have beefed up patrols.
This part of West Yorkshire, on the outskirts of Bradford, seems quiet, but has seen an unusual number of burglaries.
Police insist that the number of burglaries in the area is falling, but add that a few prolific burglars in the past have affected the figures.
Distraction burglaries are a particular problem here, where homeowners are targeted by criminals who talk their way into a property, and then distract the homeowner while they steal valuable belongings. The victims in these cases tend to be elderly and vulnerable.
This is another busy postcode in East London, with a high turnover of residents, making it easy for burglars to operate.
It is among Britain's less affluent areas, with problems with street crime and anti-social behaviour, and opportunistic burglars are known to operate locally.
Burglary has recently been identified as a priority crime in this part of Doncaster, along with spots of anti social behaviour and problems linked with drug use.
The police are working to encourage better security measures to combat professional burglaries targeting the most vulnerable homes.
This is a very diverse area, with the posher streets proving rich pickings for career burglars. The postcode area is also home to some areas of real deprivation, and within one of the estates in particular there is a real problem with crime.
It's also on the doorstep of Stretford - where Katie Price once tried her hand at politics
The former home of West Ham's Bobby Moore (pictured moving in) is another high placing on this list for East London.
It’s a busy area, with a reasonably high turnover of residents, making it easy for burglars to pass undetected.
One recent trend has been the targeting of Asian families for their family jewellery. Police are now suggesting that anyone with valuables like this at home should invest in a home safe - and improve the overall security of their property
East of London, and home to the famous Ford plant, is the nation’s overall burglary claim hotspot.
Theft has been a long-term problem in the area, and police say it’s impossible to pinpoint exactly why. They suggest a number of career criminals, ineffective security, and people storing valuables at home could be contributory factors.