ST. LOUIS — For decades, a bizarre linoleum mosaic embedded in the asphalt at Sixth and Olive streets in downtown St. Louis had people wondering: "What is it?"
The question now: Where is it?
This summer, someone used a putty knife to pry up and make off with one of the city's two remaining "Toynbee Tiles."
The tiles, with their cryptic message "Toynbee Idea In Kubrick's 2001 Resurrect Dead On Planet Jupiter," were placed here about 25 years ago.
They first appeared in Philadelphia in the early 1980s.
They became an international phenomenon and are now found on the streets of more than two dozen cities in North and South America.
The tiles, about the size of a license plate, have proven to have a powerful allure, generating websites devoted to theories about their origin and meaning.
Last year, the documentary "Resurrect Dead: The Mystery of the Toynbee Tiles" won the directing award at the Sundance Film Festival.
The movie helped popularize the artwork but may have had the unintended consequence of making them the target of scavengers, if not art thieves, as Kelley Huonker, of south St. Louis, learned to her dismay this summer.
Huonker, 30, became fascinated with the tiles after seeing the film.
"It was exciting to learn that St. Louis had some of these incredible objects," she said.
In August, Huonker and a couple of friends came downtown to see the tile at Sixth and Olive.
But where the artwork had been, they found only a blank, black square.
A security guard working nearby broke the news: A man had taken the tile just a few days earlier.
"(The guard) said he asked the guy what he was doing, and the guy said that a documentary had been made about these things and they're going to be worth a lot of money someday," Huonker said.
"I almost cried. It's terrible that someone would take it away for monetary value and rob the city of something so unique and intriguing."
Other cities where the linoleum-and-tar creations were placed include New York, Boston, Washington, Baltimore, Cleveland, Indianapolis and Kansas City. They are also found in Brazil, Argentina and Chile.
They appear to be made of asphalt crack filler, glue and linoleum and covered with tar paper. Heat and pressure from vehicle tires melds the tiles into the asphalt. The message appears as the paper cover disintegrates.
Most of them include references to English historian Arnold J. Toynbee, whose theory on regenerating dead molecules surfaced in Kubrick's film "2001: A Space Odyssey." Some of them contain political rants and demands that others "must make and glue tiles!!"
In recent years, copycats have heeded the call to make more tiles. Several examples placed in St. Louis and other cities bear the ominous message: "House of Hades Tiles Made From the Ground Bones of Dead Journalists." (One such tile is in front of Left Bank Books at 10th and Locust streets.)
The largest stock of original Toynbee Tiles, about 100, is in Philadelphia, according to Steve Weinik, one of the researchers and subjects of the film "Resurrect Dead."
The film details the sleuthing that led to the identity of the recluse, Sevy Verna, who created the tiles and how he managed to safely place them in such dangerous locations as freeways and the entrance to the Holland Tunnel in New York City.
Weinik, 33, said people have begun taking tiles in Philadelphia, as well.
"A pair of guys has been spotted prying up several here," he said. "I've been periodically checking eBay to see if any have come up for sale but so far I have not seen any. That's not to say that the thieves aren't just sitting on them for now."
At one time, St. Louis had four of the tiles. In 2009, the city paved over two of them, both on the south side of the intersection of Seventh and Market streets.
The last tile, disintegrating but still legible, is in the crosswalk at Eighth and Market streets, just outside the boundaries of the officially sanctioned art in Citygarden.
Amateur photographer and downtown attorney Bob Crowe has been a Toynbee Tile devotee for years.
He has treated the tiles as local treasures and must-see stops on tours for out-of-town friends.
"I'd like to see gold chains put up to preserve the last one," said Crowe, 62, of Webster Groves. "It represents a unique and original form of outsider street art that is an intense expression of an individual and one of the city's important cultural artifacts."
Todd Waelterman, the city's streets director, held out the possibility of saving the last Toynbee Tile.
"I am open to the idea of preserving it," Waelterman said. "If some group wants to have us hammer it up and preserve it, I have no problem with that."
He suggested a place for it.
"It's so close to Citygarden already and those people are into art," he said. "Maybe we could pick it up and move it there."