Darren Rovell joins SportsCenter to explain why Beckett Grading Services rejected several redemption cards after recipients became suspicious of the authenticity of Dak Prescott's autograph. (1:20)

Dak Prescott is being accused of using a machine to sign his autograph for a memorabilia company instead of signing by hand.

Beckett Grading Services, which evaluates and values trading cards, has refused to verify the Dallas Cowboys quarterback's signature in a recent card set.

Steve Grad, principal authenticator at Beckett, said his company looked at five autographed cards from collectors who received Prescott autograph redemptions from Panini's 2016 Prizm set.

"They had a very machine-like feel," Grad said. "You could see the starts and stops."

Signatures on some Dak Prescott cards are not being authenticated by Beckett Grading Services. Beckett Grading Services

The lack of natural flow associated with organic signatures led to Grad's conclusion that they were done by autopen, a machine that politicians have used to sign documents in bulk since the late 1950s.

"I immediately knew they were autopen," Grad said. "I've never heard of a modern athlete doing this."

It's possible that Prescott never saw the cards, as blank labels to be signed and even cards themselves are often sent to marketing agents first.

When Panini sends cards or memorabilia to be signed by an athlete, it requires the athlete to sign an affidavit stating that what it is returning is genuine.

Attempts to reach Prescott, his agent Jeff Guerreiro and his marketing agent Peter Miller were unsuccessful.

Messages left for Panini officials also went unreturned.

In May, Panini said it had discovered that some of the autographed cards of Atlanta Falcons first-round draft pick Takkarist McKinley were not actually signed by him.

The company promised to send authentic autographs to customers who returned their signed McKinley cards.