Ominous warning behind bizarre sign left on the door of an ordinary house

A homeowner has been warned their house could become a target for thieves after a sign in the shape of an X was mysteriously left on their front door. 

The mysterious symbol, which was made out of a pair of leaves, was stuck to the flyscreen door of the home at Slacks Creek, in Brisbane's south, on Saturday. 

Alex Munroe, who lives in the house, said he went out in the morning and found the X sign when he came back a little while later. 

He took a picture of the sign and uploaded the image on Reddit to ask others if they were aware of what it meant. 

'Someone's left an X made out of leaves on our front door,' he wrote. 

'Neighbors didn't see anything, and most likely it's just some kids messing around, but wanted to ask if anyone else has come across something similar or heard of an occurrence like this.

'Wondering what we might need to be planning for. 

The post was flooded with hundreds of comments from social media users, who suggested that someone might have made the symbol to check if anyone lives in the property. 

'At a guess I'd say it is a burglar, but not in the way people think,' one wrote. 

'They're marking a house to see if you remove it. If it's not removed, they'll know that the occupants are away.'

Others said the sign is commonly used in many European and Mediterranean cultures when someone visits a friend, but the home is empty. 

'My grandparents do something similar to let their friends know they’ve visited while nobody was home,' one wrote. 

'Old neighbourhood with Italians Greeks or similar?' another asked. 

'This was an old way of saying that you stopped by your house.'

Some said it could just be a harmless prank and saw the funnier side by suggesting it might be an invitation to take part in a game. 

'The start of a Tic-tac-toe game. Put a 0 below it,' one wrote.