Marty Stuart began fishing guitar picks out of trash cans as a 13-year-old mandolin player touring with bluegrass pioneer Lester Flatt. What started with castoffs grew into a 20,000-piece collection that includes an Elvis Presley sweater and Johnny Cash's handwritten lyrics to "Folsom Prison Blues" and "Man in Black."

Stuart, now 50 and a Grammy-winning country musician, pulled together most of his collection scouring Nashville pawn shops in the early 1980s. He picked up one of Patsy Cline's old stage costumes for $75 that way.

"In those days nobody cared about this stuff," Stuart says.

His collection is now worth millions and fills a warehouse in Hendersonville, Tennessee. Three hundred pieces from it, including the Cash lyrics, are currently on display at the Rock & Roll Hall of Fame & Museum in Cleveland, Ohio.

Are memorabilia like Stuart's a serious investment? Only if you have serious time and money to devote to your collection. Tales abound of collectors shelling out six-figure sums for Stratocasters supposedly strummed by Keith Richards that, it turns out after the check has cleared, came no closer to the Rolling Stone than an enterprising roadie.

Such risks aside, to rock aficionados owning a guitar used by John Lennon resonates in a way that looking at a Monet or Fabergé egg never will. That has sent prices of rock memorabilia soaring. No indexes track this market, but as an indication of how quickly prices have risen lately, a Jimi Hendrix studio guitar that sold for $130,000 in 2004 changed hands last year for $480,000.

Christie's sold the guitar George Harrison used on the Revolver album and in the Beatles' live performances for $567,000. As proof that no memento is too trite to collect, a bidder recently offered $900 for a bank check that the late Beatle signed in 1971.

As with all collectibles, the market for rock memorabilia is governed by greater-fool economics: Items are worth what someone else will pay for them. Blackie, a guitar Eric Clapton played during the 1970s, sold at a charity auction for $959,000.

An Ebay merchant is asking $4,000 for lithographs of Beatles album covers purportedly signed by the Fab Four. Another seller seeks $14,000 for a guitar he claims was signed by Paul McCartney. Both say they have letters proving the items are the real deal.

The market for bogus rock memorabilia is so big that it has even spawned a backlash of vigilantes who've taken it upon themselves to police it. One is a roadie in New Jersey, who does not want to use his name but makes guitar picks for Ozzy Osbourne and other stars. He says he often discovers fakes on Ebay and maintains a Web site, Jeremy's Rock Pages, to highlight them.

"These guys [Ebay sellers] are clearing over $1,500 a month," he says.

Ebay does not examine collectibles posted on its site and "relies on sellers to be truthful and honest and actually be selling legitimate items," says a spokesperson. If the company learns items are bogus, it pulls them from its site and alerts law enforcement, she adds.

Formal authentication became big business in the 1980s, when seals of approval helped baseball cards and other sports memorabilia jump in value. Even so, a group of forgers vouching for fake goods, in cahoots with shady retailers, pawned off $100 million worth of fake collectibles on unsuspecting buyers before they were collared by the fbi in 2000.

One sort of rock collectible that it's probably best to steer clear of altogether: autographs.

"They're too easy to copy or just create," says Terry Stewart, president of the Rock & Roll Hall of Fame & Museum. He's cautious in particular about items supposedly signed by all four Beatles. Real ones are rare, he says, and fakes are a favorite of forgers because of the sums they can fetch.

Sticking to the $30 million (retail value) auction house market is probably the easiest way to avoid the most egregious frauds. If you buy elsewhere, it's good to get a detailed ownership chain from the seller, rather than relying solely on an authenticator, says Darren Julien, president of Julien's Auctions. Look for specifics, like photographs of a musician playing the instrument.

Better still is an item that has been displayed in the Rock & Roll Hall of Fame & Museum or the Experience Music Project in Seattle. Both delve into the history of the items they display, frequently contacting artists or their estates and getting them to vouch for the collectible in question. The museums' seals of approval can double what you'd pay for a similar item backed only by an authenticator's certificate.

The Hall of Fame once declined to display a 1957 Chevrolet the seller claimed Ringo Starr had owned, when it discovered the vehicle was never registered in the rock star's name. But museums can be fooled, too. The Experience Music Project once bought a Nirvana poster that turned out to be a high-quality fake (it realized its error before displaying the poster).

For collectors in love with rock music, rather than its stars, vintage guitars are worth a look, even if they never supposedly toured the Delta with Muddy Waters. Instruments that have survived since the 1950s and 1960s in prime shape can fetch five or six figures.

Vintage Guitar magazine lists 1963 vintage Gibson sg custom guitars at up to $22,000. A Gibson Les Paul Standard with a sunburst decoration goes for $350,000. Musical instruments are harder to fabricate than signatures.

The market is so hot that Thomas Byrne, cofounder of London's Anchorage Capital Partners, thinks he can raise $100 million for a closed-end fund that will buy vintage guitars and rock memorabilia. "Prices have never gone down," he insisted in October. Since then, new figures have come out showing that over the past year the market has declined 7%.

By David K. Randall