PHILADELPHIA - A U.S. Marine who brought home seemingly cheap souvenirs from Iraq has turned them over to authorities after learning they are ancient stone seals used as signature stamps.

The Marine paid a vendor a few hundred dollars for the eight seals, and had them examined by a university archaeologist upon his return.

The seals, which were looted from an archaeological site near Babylon, are about 5,000 years old and valued at $2,000 to $5,000 each.

In Mesopotamia, families rolled the cylindrical seals onto clay tablets to stamp their signature image - perhaps a graphic or animal design, akin to a coat of arms - onto legal documents, said FBI Agent Bob Wittman, who works on a new FBI art-theft task force.

"There are many of these, but they're all a piece of their history," said Assistant U.S. Attorney Bob Goldman, another task force member.

Experts say many ancient sites in Iraq have been looted since the fall of Saddam Hussein, who threatened looters of antiquities with the death penalty.

U.S. soldiers are allowed to bring back souvenirs and trinkets, but are not supposed to bring back antiquities, Goldman said.

"As soon as he realized (their worth), he felt bad about it. He reached out," Goldman said of the Marine, who was not identified by the FBI.

Samir Sumaida'ie, Iraq's ambassador to the United Nations, plans to loan the set to the University of Pennsylvania Museum of Archaeology and Anthropology in a ceremony Wednesday.