Scratched onto pavements, walls, and doorways, these symbols are small enough to go unnoticed - and innocent-looking enough to be dismissed as nothing.
But, last year, police in West Yorkshire uncovered a series of coded chalk symbols which criminals are using to tip off other criminals.
And they’ve now started appearing around Warwickshire, including outside the home of an elderly woman who was recently burgled.
“If you see any unusual markings on your home, low rise walls, pavement, kerbs or bins, take a photo, remove them and contact us"
Last year, police shared an image - exposing the ‘Da Pinci Code’ in full - to Facebook.
An open book is used to show that a woman is living alone, whilst two squares overlapping one another shows that the homeowner is nervous or afraid of thieves.
At the time, they said: “If you see any unusual markings on your home, low rise walls, pavement, kerbs or bins, take a photo, remove them and contact us.”
Now, following the recent spate of burglaries and chalk markings, police have urged homeowners to be vigilant when it comes to strange markings.
PC Craig Purcell told the Coventry Telegraph: “Whilst a certain criminal element make use of these chalk marks there are of course other reasons they may appear.
“I have previously known them attributed to scouts, brownies, running groups, utility and maintenance companies and kids.
“Not all chalk markings have been put there by criminals identifying property as a likely target so we do not in any way wish to scare or worry residents.
“Regardless of how the reported symbol occurred it is always worthwhile alerting our communities to suspicious incidents.”
**If you are a Warwickshire local, and you spot one of these marks near your home, please contact police on 01789 444670. **