The cards contain a chemical that replicates the smell of the plants when they are growing.
Photo credit: CrimeStoppers
Scratch-and-sniff cannabis cards are being handed out by police in Avon and Somerset to help members of the public detect drug farms.
In 2011-12, the number of cannabis factories rose by 15 per cent and they are increasingly being set up in residential areas.
Hot spots targeted in the Crimestoppers campaign include West and South Yorkshire, London, Greater Manchester and Avon and Somerset.
The cards being handed out contain a chemical that replicates the smell of the plants when they are growing.
Roger Critchell from Crimestoppers said: "Not many people know how to recognise the signs of cannabis cultivation which is increasingly happening in their neighbourhood, many are also not familiar with the established links between this crime and serious organised crime."
A report for the Association of Chief Police Officers (Acpo) last year found that cannabis farms are increasingly being set up in residential areas.
Andy Bliss from Acpo said: "Closing down cannabis farms and arresting the criminals who run and organise them is a key focus in drugs policing.
"This is because we recognise that these farms are often run by organised criminals but also because they bring crime and anti-social behaviour into local communities causing real harm and leaving people feeling unsafe."
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