Al Brandtner's artwork, titled 'Patriot Act.'

CHICAGO — The Secret Service sent agents to investigate a college art gallery exhibit of mock postage stamps, one depicting President George W. Bush with a gun pointed at his head.

The exhibit, "Axis of Evil: The Secret History of Sin," opened last week at Columbia College in Chicago. It features stamps designed by 47 artists addressing issues such as the Roman Catholic sex-abuse scandal, racism and the war in Iraq.

None of the artists is tied to the college.

Secret Service spokesman Tom Mazur would not say yesterday whether the inquiry had been completed or whom the Secret Service had interviewed, but he said no artwork had been confiscated.

The investigation began after authorities received a call from a Chicago resident.

"We need to ensure, as best we can, that this is nothing more than artwork with a political statement," Mazur said.

Two federal agents arrived at the exhibit's opening night on April 7, took photos of some of the works and asked for the artists' contact information, said CarolAnn Brown, director of the Glass Curtain Gallery.

Brown said the agents were most interested in Chicago artist Al Brandtner's work titled "Patriot Act," which depicted a sheet of mock 37-cent red, white and blue stamps showing a revolver pointed at Bush's head.

Brandtner did not return a call to his design studio yesterday.

The exhibit's curator, Michael Hernandez de Luna, said the inquiry "frightens" him.

"It starts questioning all rights, not only my rights or the artists' rights in this room, but questioning the rights of any artist who creates — any writer, any visual artist, any performance artist. It seems like we're being watched," he said.

Last spring, Secret Service agents in Washington state questioned a high school student about anti-war drawings he did for an art class, one of which depicted Bush's head on a stick.