Burglars are leaving stickers on the front doors of people’s homes to mark them as possible targets for break-ins, police are warning.

The tiny transparent stickers advertise “24-hour locksmith” and police believe “scouts” are leaving them on properties considered easy to burgle.

Detectives in Wandsworth have discovered dozens of the stickers on front doors but the telephone number on the label does not exist.

The scouts call at addresses to see if people are at home during the day while also checking out doors, windows, locks and alarms. If they think the home would be easy to break into a sticker is left on the door. If they are stopped by the police they can claim to be innocently distributing marketing material.

Wandsworth council’s crime prevention spokesman Jonathan Cook said: “There is growing evidence that some organised teams of burglars may be using this method to target homes in south London. We are therefore urging local residents to keep a very close eye out for these stickers and if they find one to remove it straight away and report it to the police.”

Police say the stickers are so discreet that residents may not even notice they are there. If they are spotted and removed then the criminals know the property is occupied. Detectives are already linking these stickers to at least one burglary in Wandsworth.

Burglars are often suspected of leaving signs on houses indicating that they are easy to burgle. Recently police in Manchester warned that criminals were leaving chalk symbols on the walls of homes, pavements and kerbs to highlight potential targets. The markings featured a series of crosses and boxes.

The alert comes as police warn that there is a traditional rise in break-ins as the nights get darker, though the latest figures show the number of burglaries in London is falling.

Inspector David Bannister from Wandsworth police said: “There have been a number of front doors found with stickers, giving details of a locksmith, which enquires reveal is not a genuine company. These are placed near the main lock.”

Police have since found similar stickers in other south London boroughs.

Mr Bannister added: “Please report any such labels found at your home address to police. Please phone 101 and ask to speak to your neighbourhood policing team.”