In the decades before the Civil War, slaveholders in this seaside city would often rent their slaves to others to work in a variety of jobs -- porters, maids, carpenters, fishermen.

The city fathers, to raise revenue and control the movement of slaves, issued metal badges for the rented slaves to wear.

The rare tags, which have brought as much as $26,000 at auction and are actively bought and sold by collectors, provide a little-known glimpse into a dark chapter of American history.

"People like the rarity," says Harlan Greene, author of a forthcoming book on the slave badges. "But I also think it is the drama, the Gothic horror in that it was worn by a slave."

One of the earliest known badges is dated 1800. Stamped on thin copper, the badges are normally square, about two inches a side, and bear the year of issue and occupation the slave performed -- servant the most common, fisherman, carpenter and mechanic more rare.

The only genuine badges are stamped with either Charleston or Charleston Neck, says J. Grahame Long, curator of history at the Charleston Museum, which has almost 50 tags, thought to be the largest public collection of the artifacts.

About 1,000 genuine badges are known to exist, but many more than that were stamped, says Greene. The tags, like license plates for cars, were issued each year for rented slaves.

"Slave tags represent a tangible relic of slavery . . . and not much else fits the bill," says Harry Ridgeway, a Winchester, Va., collector and dealer. "Even though there are no names on them, the numbers did represent a real human being."

Charleston was not alone among Southern cities having laws regulating urban slavery. Richmond, Savannah and Wilmington had similar laws, Greene says, but if they used slave tags, they didn't survive.

"It gives the slave some power as to being his own boss, and that's why so many people reacted so strongly against them. They didn't like the idea that slaves could walk around," Greene says.

Much of the opposition to the tags was from working-class whites who felt their jobs could be threatened by skilled, badge-holding slaves.

"They would petition the city, and the city would basically say, 'We're a slaveholding people and there is nothing more important than not to interfere with the rights of a slaveholder and his slave. That's sacred," ' Greene says.

Recent interest in the badges, particularly trade among collectors on the Internet, has resulted in numerous fake tags.

With tens of thousands of the genuine badges apparently stamped, and only a relative handful found, where are the rest? Because former slaves generally threw away the badges after the Civil War, many might still be buried in yards and building sites in Charleston, experts say.

And treasure hunters are trying to find and sell the tags, Greene says.

"There are numbers of dishonest people in this town who jump fences at night and get on other people's property," he says. "It's easy. It's quick and dirty. It doesn't take any particular skill if you have a metal detector."

Charleston Museum curator J. Grahame Long holds up a slave tag.