Warning: burglars may be watching your house

You probably wouldn't think twice if you happened to notice a few white stones outside your house or tucked underneath the wheels of your car - it's the sort of thing a child might easily do.

But a neighbourhood watch in Bristol is warning that you should be on your guard, as it could be a sign that your home is being scoped out by burglars.

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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."

Why burglary victims are targeted again - several times

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?

White stones
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.

Overlapping squares
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.

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Flower petals
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...