PIERRE, S.D. (AP) - State and federal officials are seeking the return of pilfered stone markers that were put in place more than a century ago to mark the border between South Dakota and North Dakota.

Possession of the pink quartzite survey markers is a violation of federal law, State Historical Society Director Jay D. Vogt said in a written statement.

"While not as fashionable as pink flamingos, the markers are winding up as lawn ornaments at an alarming rate," Vogt said. "Although people adorning their lawns with the tacky pink birds may be guilty of bad taste, those possessing the pink quartzite markers are guilty of violating federal law."

The markers, more than 7 feet long, were placed along the border in 1891 and 1892. The markers are under the jurisdiction of the federal Bureau of Land Management, and the removal or possession of the stones violates several federal laws.

The markers were sunk more than half their length into the ground and were placed every half mile along the border between the two states. Officials estimate that more than half the 720 markers have been removed.

Some of the stones were removed during road construction while others were collected by adjoining landowners, according to officials. Many are scattered throughout people's yards and small-town museums in North Dakota and South Dakota.

The BLM is not out to punish well-intentioned people who possess the survey markers, but the agency is asking people to voluntarily return the markers without penalty, said special agent Brian Cornell.

"In cases where the law wasn't purposefully broken, we can pursue civil reconciliation as a mitigating solution," Cornell said. "Civil reconciliation can entail returning the markers to public use without pursuing criminal charges."

However, anyone removing the markers for private use or sale could be charged with a crime.

A replica of the markers is the traveling trophy for the winner of the North Dakota State University-South Dakota State University football game.

Cases involving illegal possession of border markers have arisen in both states in recent years.

Fargo, N.D., police in 2005 confiscated a marker from a former North Dakota State football player who had found it near his family's ranch. The marker was released to the BLM, which agreed to turn it over to NDSU for display on the campus. The former football player was charged with possession of stolen property, but that charge was later dismissed.

Two markers in Corson County, S.D., were recently returned by a local landowner who had been unaware that possession of the stones was illegal. No charges were filed.

Ken Stewart of the State Historical Society Archives said state and federal officials are focusing their efforts on educating the public on the need to return and protect the markers.

"We get three or four calls every year about the markers," Stewart said. "Usually someone's unhappy that someone else has removed one and relocated it to their yard and made it into a birdbath. People just don't recognize the significance of the markers."

Those wishing to return markers can call the BLM at 406-896-5010, the South Dakota State Historical Society at 605-773-3458, or the North Dakota State Historical Society at 701-328-2672.