Liza Minnelli fans who bought signed copies of her memoir are seeking refunds because they believe her signature is fake.

Copies of Kids, Wait Till You Hear This! by the American 80-year-old singer were marketed around the world as “hand-signed collectibles”, with premium editions costing up to $250 (£185).

However, some buyers have questioned the uniformity of the signatures and speculated that they were digitally signed by an autopen, a device that replicates handwriting.

“When you see footage of Liza today in her own documentary, she is far too frail to have signed a handful of books this accurately, let alone hundreds,” said autograph collector Gareth Brown, who contacted the Guardian after paying £25 for a signed copy in a Kent bookshop.

He said he bought the hardback rather than waiting for the cheaper paperback edition because of the signature.

“I started wondering how many books she must have signed for one to end up in an independent bookshop at an English seaside,” he said. “I found there was much online discussion about this and many photographs of the signature, all of which look the same.”

Fans, armed with tracing paper overlays, have turned sleuth and concluded that the signatures in their books are unnaturally identical.

According to Justin Steffman, the CEO of autograph authentication service AutographCOA, none of the examples he examined appear to have been signed by a human hand.

“It has sadly been common for many celebrities to sell ‘signed’ merchandise featuring fake signatures,” he said. “So uncovering that Liza Minnelli’s memoir features what looks like autopen-signed autographs was no surprise.”

Fans posting online have said they intend to return their copies.

Minnelli is a singer, dancer and actor and daughter of the late Hollywood star Judy Garland. She made her screen debut as a toddler. Earlier this year she released her first new music in 13 years, adding vocals to an AI-created dance track.

Minelli’s agent and US and UK publishers Grand Central Publishing and Hodder did not respond to the Guardian’s request for comment. Grand Central Publishing previously told the entertainment website Radar Online that all copies of the memoir had been signed by the author.

The autograph market is estimated to be worth more than $25bn worldwide, but collectors are being warned to be wary of fakes. In 2022 Bob Dylan was forced to apologise after copies of his book sold as hand-signed at $599 were revealed to have been signed by autopen.

The previous year, Sinéad O’Connor admitted to using a stamp to sign 10,000 copies of her memoir, Rememberings.

“Hundreds of top entertainers and celebrities have used autopen machines (and assistants) to sign their merchandise in the past and unfortunately will continue doing so,” said Steffman.

Brown said he wrote to Hodder asking if the signature was digital but received no reply.

“I feel deceived,” he said. “What I value about autographs is that they capture a moment in time of someone I admire, it’s for ever there just a second or two. In this case, though, I feel robbed.”