It might have looked like performance art. But the people dressed as Secret Service agents who showed up at an exhibit opening on Thursday at Columbia College Chicago were the real thing -- sent to follow up on complaints about the art.

The exhibit is "Axis of Evil: The Secret History of Sin," which features images created on fake postage stamps. The Secret Service agents were apparently most interested in a work called "Patriot Act" that depicted a sheet of stamps showing President Bush with a revolver pointed at his head. The exhibit is on display at Columbia's Glass Curtain Gallery through May 11.

The Secret Service agents asked the gallery's director for the phone numbers of all 47 artists in the show, and the director refused, a Columbia spokeswoman said. The agents then took photographs of the art and left.

Jonathan Cherry, a spokesman for the Secret Service, said that the agents acted after receiving a complaint from a private citizen. "The Secret Service certainly respects artistic freedom, but we must look into exhibits when necessary," Cherry said. He said he was not sure if the investigation was complete, and stressed that "we haven't confiscated anything."

Micki Leventhal, the college's spokeswoman, said that officials there would defend the gallery's right to hold the exhibit. "We support freedom of speech and we stand for academic freedom," she said.

Leventhal said that the controversy broke during a visit to campus by John Frohnmayer, a lawyer who was head of the National Endowment for the Arts under the first President Bush, and who had to defend the endowment amid controversy over its support for galleries that displayed such works as "Piss Christ."

Frohnmayer visited the Columbia exhibit and advised the college that everything there was protected by the First Amendment, Leventhal said.