The gun-control activist whose provocative billboards have been turning heads along the Massachusetts Turnpike for 13 years today will unveil one of his most eye-popping messages yet - a fake neon advertisement for American gun shows where people can buy weapons, no questions asked.

"We Sell Guns! No ID required. No background checks. Criminals and terrorists welcome!" the billboard peals.

"Gun shows are the equivalent of Al Qaeda terrorists walking directly onto the airplane while you and I wait in the TSA line," John Rosenthal, founder and chairman of Stop Handgun Violence, said in a recent interview. "They don't want us to go on airplanes but they let Al Qaeda buy guns unprotected."