WASHINGTON - They are some of the rarest bobblehead dolls ever produced. They're released erratically. They're given away for free, not sold. And if you get a certificate to claim one, you have to redeem it at a Washington law office.

The limited-edition bobbleheads of U.S. Supreme Court justices are the work of law professor Ross Davies, who has been creating them for the past 10 years. When finished, they arrive unannounced on the justices' desks, secreted there by unnamed confederates. And fans will go to some lengths to get one.

"I think we take seriously trying to do them well," said Davies, a law professor at Virginia's George Mason University and the editor of a quarterly legal journal, The Green Bag.

Subscribing to the journal is the most reliable way to get a voucher to claim a bobblehead, but there's no guarantee. The certificates warn that the bearer "might be able" to exchange it for a bobblehead, and the journal also hands out some dolls to non-subscribers, including law school public-interest groups that auction them at fund-raisers. Some ultimately wobble their way onto eBay, where they sell for hundreds of dollars.

The justices seem to have been charmed by their caricatures. Antonin Scalia once said that he understands his is the most popular. Stephen Breyer had four of the figures of his colleagues on display in his chambers during a 2009 C-Span interview. His own is in the works. And former Chief Justice William Rehnquist sent a thank-you note for his, which was the first to come out in 2003.

"Thank you for the 'bobble-head' likeness of me which now sits on the mantle of the fireplace in my chambers," Rehnquist wrote. "It is probably a better likeness of me as I was 15 years ago than as I am now, but obviously I won't complain."

Davies said the idea for the bobbleheads came to him in the shower. He has immortalized 16 justices in ceramic, including four of the current court's nine members. Included in that total are a set of miniature bobbleheads representing the first justices appointed to the court. Certificates for the newest tiny justice, John Blair, recently went out.

The dolls, which are produced by Bellevue, Wash.,-based Alexander Global Promotions, are more than straight likenesses of the justices. Each has multiple references to the legal legacy of the person it honors.

For example, Justice Louis Brandeis rides a train, a nod to his important opinion in a case involving the Erie Railroad in Pennsylvania. The David Souter bobblehead plays a song by "Modest Mouse," a group he mentioned in a copyright case.