For the small but maniacally devoted art-and-cryptography community, this was a landmark weekend, as artist Jim Sanborn took to the New York Times to throw a bone to codebreakers looking to unlock the riddle of his 1990 sculpture for the CIA's headquarters, "Kryptos." The outdoor installation, located in the agency's courtyard, consists mainly of a curving copper plate inscribed with some 1,735 characters, which contain no less than four encrypted messages. The first three were cracked by a CIA physicist in 1998. The mysterious "Panel 4," designed to be especially difficult to crack, has continued to stymie sleuths. Sanborn, apparently growing weary of fans confronting him with false solutions to the 20-year-old puzzle, has decided to push the process along by offering a hint.

The clue? "BERLIN," a word that evokes the CIA's many exploits in the Cold War espionage capital. This, the artist says, is the meaning of the final six characters of the sculpture, which read "NYPVTT." The revelation might well help fans develop a key to solve the riddle of the other 91 characters.

Contracted by the CIA Fine Art Commission for $250,000, "Kryptos" was part of an expansion into new headquarters, paid for by a federal percent-for-art mandate. The installation includes a petrified tree — meant to represent the "source of materials on which written language has been recorded" — and a bubbling pool of water symbolizing "information being disseminated with the destination being unknown," according to an official "Kryptos" Web site.

The intrigue of the work, however, has always derived from the secret messages themselves, devised by the artist with the help of CIA cryptographer Edward Scheidt. "Kryptos" has garnered a substantial cult, particularly after author Dan Brown referenced it in his 2009 novel "The Lost Symbol," suggesting (erroneously) that it might contain "ancient Masonic secrets."

So far, no new solutions have been posted on the most popular "Kryptos" fan site, maintained by Elonka Dunin. For those who think they have cracked the code, Sanborn maintains a special Web portal where people can send their solutions.

Then again, it's possible that even after the code is cracked, the intrigue will continue. "Once the plate is deciphered I'm not convinced the true meaning will be clear even then," Sanborn said in a 1991 World News Tonight interview. "There's another deeper mystery."

Update: Elonka Dunin writes Artinfo to say: "it's a significant clue, and we've made someinteresting discoveries over the last 48 hours. If you'd like tofollow along, send an email to kryptos-subscribe@yahoogroups.com."