Pampas grass, trainers and other urban codes

TV PRESENTER Mariella Frostrup found herself on the end of some unwanted advances from swingers after putting two pampas grass plants on the balcony of her flat in west London, it was reported this week. It seems that she was unaware that the plants had sexual connotations and are used as a code.

Frostrup, who lives with her husband and two children, said she only realised what she had done when a friend explained the hidden meaning over dinner. She told the BBC: "What I found out was that I had actually signposted my flat on both sides as a swingers' paradise."

However, modern life is full of such secret codes. Here are others to watch out for:

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• Shoes hanging from wires: A pair of trainers with the laces tied together and slung over a telephone wire is now a common sight in cities around the world. But their meaning has many different interpretations. Most are to do with gang activity in the area. The shoes may signal that drugs can be bought at the spot or in a nearby house, mark the boundaries of a gang's territory, or mark the spot where a gang member died.
• Ghost bikes: These are roadside memorials for cyclists who have been killed or injured nearby. Ghost bikes are usually old machines that are then sprayed white and chained to railings, sometimes with a placard attached. The phenomenon emerged in America in the early 2000s and quickly spread. The white bikes also serve as a warning to other cyclists and motorists.
• Handkerchief code: Secret signals abound in the gay community, most of them dating back to the days when homosexuality was frowned upon. Some of the most elaborate concern the use of handkerchiefs of different colours displayed in different ways to indicate a sexual preference. Meanings vary between regions but there is broad agreement on some things. For example, a black bandana signifies a keenness for S&M.
• Yellow ribbons: The tradition of tying a yellow ribbon around a tree is well known as a sign that the occupant is awaiting the return of a loved one. These days it is particularly associated with the armed forces, but also applies to the loved ones of prisoners. It is thought the practice has a long history: it has even been claimed that a mural at the Roman city of Pompeii, destroyed in AD79, featured a man next to a tree with a yellow ribbon tied round it.
• Graffiti: Walls are the perfect place to leave coded messages - and cities are now awash with signs that often don't mean much to the uninitiated but are full of hidden meanings. Graffiti can indicate the boundaries of a territory, carry a threat or a warning or be used as an invitation to a secret event. Competition among graffiti artists to stand out is fierce. In Berlin, one artist has been painting pictures of boom boxes on walls with a 'QR code' where the tape would sit. Fans with smartphones track down the images, scan the QR code, and can then listen to music.