Los Angeles, California (CNN) -- Michael Jackson's three children did something recently they've never before done: signing their autographs on something to be sold.
Blanket, Paris and Prince Jackson put their names on a designer belt produced as a tribute to their late father and to raise money for the Jackson family museum planned for Gary, Indiana.
The merchandising deal for the crystal-encrusted belt is also a first -- the trustees of the Michael Jackson estate authorizing the Jackson family to produce and sell memorabilia in the pop star's name.
Katherine Jackson dropped her challenge for control of her son's estate last October, but her husband still has a legal objection pending in probate court.
"This is a truly one-of-a-kind opportunity," said Jerry Olivarez, the Jackson family friend who brought the deal together. "I know of no other item that has ever been made available to the public that has been signed by both the parents and children of Michael Jackson."
The youngest, who was born in 2002, signed his name in true "John Hancock" style, taking up the most room with large block letters spelling "BLANKET."
Prince, 13, helped his younger brother by adding "Jackson" below his first name.
Paris, 12, showed flair with her signature, using a heart to dot her "i" and giving her "r" a long, flowing branch.
Grandparents Katherine and Joe Jackson sat next to each other on a sofa in the Jackson's Encino, California, home to add their autographs to the "artist proof" of the belt.
The leather belt was designed by Simon Tavassoli and a limited run of 7,000 are being handmade at his Newport Beach, California, studio. Each unsigned belt will retail for $1,500, he said.
The only belt signed by the three children goes on auction Thursday night, Tavassoli said.