By Chris Heard BBC News Online entertainment staff

It is the British modern art world's greatest guessing game - and the prizes can be financially rewarding.

See a selection of the Secret postcards In pictures

Located somewhere among the 2,600 postcards on sale at �35 each are creations by luminaries such as Damien Hirst, Tracey Emin, Julian Opie and Sir Peter Blake.

Others have been made by fashion designer Alexander McQueen, Wallace and Gromit creator Nick Park, Monty Python's Terry Gilliam and Turner prize nominee Grayson Perry.

The catch is that you do not discover the artist's identity until you have handed over your money - so your potential one-off Britart rarity could turn out be the work of an unknown postgraduate student.

Never mind, say organisers of the Royal College of Art's annual fund-raising "Secret" sale, now in its 10th year. After all, that is not really the point.

"It's best to buy what you like," said Glynn Williams, head of fine art at the college in Kensington, London.

"Some artists will add their own thing and it leaps out at you who it is. But a lot of young contributors are impish in their imitation of known artists, so the one you choose may not have a sell-on value."

The postcards are signed only on the back

Hundreds of RCA students and former students have joined an international castlist of artists, designers and illustrators involved in this year's sale.

Backed by David Bowie (a former contributor) via his website, it is expected to raise up to �100,000 to fund student art projects.

The postcards, on display in blocks of 100, represent a vast range of styles and disciplines, from traditional painted portraits to lively abstract works, as well as collage, graphics and photography.

They contain a bewildering array of themes, many focusing on social issues, consumerism, the media and politics, the environment, sex and religion.

Many are amusing and witty; others bleak and uncompromising. Some seem to seek shock value; one or two are pornographic.

There is huge variety and what soon becomes an overload of visual information for a single visit.

A Peter Blake rarity - or the work of an unknown student?

At random, they include: A simple vertical stripe of red paint on a white card background; a beach collage using pebbles, seaweed and tiny shards of driftwood; a photograph of a pair of feet in socks and slippers.

A slogan reads: Nothing Really Matters. Another: Sting makes me throw up.

There are miniature oils of cityscapes and watercolours of churches; two coloured paper circles pasted on a surface; pieces of a burst pink balloon stuck to another; an Elvis image composed entirely of coloured plastic beads.

But which of these is a one-off Emin original capable of turning your �35 into �3,500 or more?

'Mind-blowing'

Austin Clarke, 53, who picked out a Damien Hirst last year, has already pitched his tent at the front of this year's queue seven days before the sale begins.

"I spent one night here last year and got a Hirst. It was mind-blowing," said Mr Clarke, 53, of Larne, County Antrim, a mechanical engineer who is married with two daughters.

"It was a lucky judgement but I didn't buy it to sell on. I liked it and even if it hadn't been a Hirst I would have bought it. I'm an art lover."

Gavin Cheung, 26, of London, who is also queuing, bought works last year by Billy Childish, Mary Fedden and David Leapman.

"It's a bit of a gamble - you are gambling using your own instinct," he said.

Buyers can view the postcards from 22 to 27 November, either at the college or online at www.bowieart.com.

The sale begins at 0800 GMT on 28 November and ends at 1800 on 29 November. Buyers must attend in person.