Pick a card, any artist's card, and it could be worth a fortune

One of the most popular guessing games in British art – the chance to buy a genuine Damien Hirst or Sam Taylor-Wood for £35, if you can spot the artists' handiwork without a signature – is about to begin again.

At the Royal College of Art in Kensington, London, yesterday, hundreds of works of art, all the size of a postcard, were being unwrapped and mounted for the ninth "RCA Secret" exhibition. Hundreds of artists, including big names in international art as well as present RCA students, have contributed one or more works on a postcard, which will be sold for £35 each to raise funds for the fine art department.

The contributors include the American minimalist artist Sol LeWitt, aged 74, British veterans such as Patrick Caulfield, and young stars such as the Tim Noble and Sue Webster partnership, and the Turner Prize nominee Keith Tyson.

Sir Paul McCartney has donated a work for the first time. The fashion designers Zandra Rhodes and Giorgio Armani, the film director Ken Loach and Terence Conran, the Habitat founder, have all done their bit. If you spot a postcard covered in plastic, it could be the offering of Christo, the artist who "wrapped" the German parliament building.

All go on display at the college from this Thursday for a week's viewing. Anyone who cannot attend can check out the 1,300 items at www.bowieart.com. The three-day sale starts on 29 November.

Last year, one woman queued for four days to snap up works, securing a Marc Quinn and a Christo, though she did not get all the big names she thought she had spotted.

Professor Sir Christopher Frayling, rector of the RCA, said: "The variety of postcards is astounding, from paintings to photographs, collage to drawings, all in miniature format."

Some enterprising contributors even used the postcard as a base to build tiny sculptural works, such as tiny Rachel Whiteread's blocks. Last year, there was even a postcard on wheels.

Emily Sargent, the show curator, said there was "a kind of democracy" in the uniform size, but it also made it difficult to guess some artists. The tiny format could disguise an artist's characteristics. The trick was not just to guess the famous names, but to select works you liked, she said.

A LeWitt could be worth thousands, yet even less well-known names might prove a hit. Someone who chose a card by Sophie von Hellerman when she was a recent student at the RCA would have seen the value of the piece rise considerably after she was showcased by the avid collector Charles Saatchi and attracted widespread critical attention.

The sale is expected to raise more than £50,000, which will go towards bursaries, travel grants and the cost of materials for the fine art students' final-year shows. More than £500,000 has been raised in the nine years since the exhibition was inaugurated.

Ms Sargent said the standard of the works was very high. "Inevitably, with a large number of pieces, there are some that aren't to my taste or are a bit weak. But there are really exciting artists this year. And it is great fun."

How to spot a Hirst: tips for the artless

So it's hunt the needle in the haystack time again. The great majority of the postcards will be worth roughly the same as the card they are presented on. But a handful of the 1,400 cards – by the likes of Damien Hirst, Sol LeWitt, Julian Opie, Sam Taylor-Wood and Christo – will be truly bankable.

How do you spot them? First, consider the nature of these works of art. Some are pencil drawings; others are done in charcoal or pen; some are painted in oils or acrylic. Yet others are photographs or photo-montages while some of the most unusual are three-dimensional.

Does this help in any way? Yes – because certain artists favour particular media.

Take Hirst. He is among the trickiest because he is always looking for ways to re-invent himself. His current preoccupations are massive, three-dimensional sculptural forms, which could be a clue to his card at the RCA.

Some artists are so recognisably themselves that they might be quite easy to spot. For example, Opie never uses a pen. All his images are computer-generated, and they are extraordinarily smooth, cool and flowing when he represents human beings.

But beware! The very fact of his "recognisability" might mean Opie has done something utterly uncharacteristic this time. He may even have lifted a pen or a brush.

The work of LeWitt, the American painter and sculptor who has been long resident in Italy, has always been characterised by a fascination with geometrical forms such as cubes that interlock. These are usually painted white, so expect something fairly minimal and relatively colourless; perhaps something which looks like a drawing-in-progress for a three-dimensional form.

Christo is a master of the art of wrapping – anything from the Reichstag to a river. This is so completely his obsession that I suspect he won't be able to avoid some variant upon the postcard-in-muffled-disguise

And Taylor-Wood? Search the photographic stills for an image that looks as if it is a frozen moment from a piece of video art. The body may be young, beautiful and in a balletic pose. Perhaps it will be in arrested motion. Hand over the cheque, cross your fingers and run.

Michael Glover