Menendez Brothers Flooded With Requests for Autographs on Eerie NBA Cards

Erik and Lyle Menendez are experiencing newfound fame behind bars thanks to the popular Netflix series about the gruesome murders of their parents ... and there's a weird request that keeps coming up in the fan mail that's been pouring in, TMZ has learned.

A source with knowledge at Richard J. Donovan Correctional Facility in San Diego tells TMZ ... the infamous brothers have seen a "huge" increase in mail from fans (and, of course, some haters) thanks to wild interest in Netflix's "Monsters: The Lyle and Erik Menendez Story."

Perhaps the most interesting item the brothers are being sent ... 1990-91 Hoops Mark Jackson NBA cards -- the brothers are on the card, snapped sitting in the Knicks crowd, after the murders, before their arrests -- and people want 'em autographed.

The brothers ... who spent years incarcerated apart before being reunited in 2018 at the San Diego prison ... were recently paid a visit by Kim Kardashian, among other high-profile names, in her quest for prison reform. Kim has since said the brothers should be set free.

As we previously reported ... the brothers are again making national headlines after L.A. County D.A. George Gascón announced prosecutors are reviewing new evidence ... and he will decide if the brothers should get a new trial, or if prosecutors should go for a new sentencing -- presumably manslaughter -- which could set them free.

Seems their story is far from over ... and the mail will definitely keep pouring in.