SECRET symbols used to alert thieves to vulnerable homes have been spotted in the city.
The codes may indicate that a home is wealthy, has already been burgled or may have nothing worth stealing.
And they may also reveal if there is a vulnerable female in the home, or if the occupant is nervous or afraid.
Neighbourhood police in Exeter have issued a warning to homeowners to be wary of the symbols.
The signs have appeared at least twice on properties in Pinhoe.
Officers believe the codes may be used by "travelling" criminals to alert other thieves to properties which present a "good target".
Police have taken to social networking site Twitter to warn residents about the codes.
One Exeter police officer told followers on the website that they had twice seen a slight variation of the "good target" symbol near a property in Pinhoe. However, neighbourhood police in the city say the use of such symbols is not "prevalent" in Exeter. But the officer tweeting from the @ExeterCityNPT Twitter account said wealthy properties could be at risk. The officer tweeted: "Not that prevalent but helpful if people aware salubrious properties could be marked."
A simple 'X' means the home is a good target, while the same symbol outlined with a circle means there is nothing worth stealing in the property.
A capital D with a dash drawn in it indicates that burgling the house is too risky, while five circles in the shape of a star shows that a property is wealthy. Other marks reveal if a house is alarmed or has already been burgled.
Police in Torbay have also posted the symbols on Twitter in a bid to warn homeowners that they may be a target for thieves. Detective Constable Steve Fleetwood warns the "ancient" symbols are being drawn outside homes by criminal gangs. He said: "The Exeter Neighbourhood Team saw them at the end of a few drives, on a few kerbs and on gate posts and we want to warn people about them."
Det Con Fleetwood added: "If we're aware of it happening we can see if there have been any burglaries in the area and we can analyse the data to gather intelligence." He urged homeowners to report unusual markings by calling 101.