The red flag might be the way the man makes a point of answering the ticket agent's questions, so the teenage girl with him doesn't have to talk.

Or the young boy doesn't know where his flight is going, and appears to be under the control of the man who claims to be his coach.

Or the girl flying alone insists her boyfriend paid for her flight, though she has never met him in person, but only on Facebook.

These are scenarios that should raise the suspicions of airport workers who are uniquely positioned to help rescue victims of child sex trafficking, local, state and federal officials told a roomful of Oakland International Airport employees on Tuesday.

The workers, from blue-uniformed Transportation Security Administration agents and baggage handlers to restaurant workers and gate agents, were taught how to recognize potential victims and their abusers, who take advantage of the fact that minors can fly without identification.

They heard from Shamere McKenzie, 30, of Chicago, a former sex trafficking victim, who warned that abused children may deny being mistreated and are psychologically unable to escape their predators' clutches. They won't, she said, go running to the first TSA agent or officer they see at an airport.

Their abusers, in turn, regard them as "commodities, a product that can be bought and sold," McKenzie said. She told the airport workers to close their eyes and picture their own children being forced to engage in sex acts. One woman, who appeared to dab at her eyes, got up and left.

Some 10 million people travel through the Oakland airport each year. Similar training was conducted at San Francisco International Airport in 2012 and at Mineta San Jose International Airport in January.

The employees were thanked by a host of leaders, including Rep. Jackie Speier, D-Hillsborough, Rep. Barbara Lee, D-Oakland, U.S. Attorney Melinda Haag and Alameda County District Attorney Nancy O'Malley.

"Modern-day slavery should never exist in the world, and especially here at the Oakland International Airport," Lee said.

Speier noted that big conventions and sporting events like the Super Bowl boost demand in host cities for illicit sexual services.

"Airports are magnets for sex trafficking," Speier said. "Keep your eyes open, and if you see something, say something."

More warning signs: a child doesn't make eye contact with anyone, an adult stares directly at a child, or a teen carries no personal items. In an extreme case, a trafficked child might have a bar code tattoo on her neck, signaling she is owned.

"It might be somebody who's not dressed for the appropriate weather for the place they're going to. They're in shorts in the middle of the winter, flying to Chicago," said Betty Ann Boeving, executive director of the Bay Area Anti-Trafficking Coalition.

Boeving said it's better to be nosy and turn out to be wrong - a child could simply be uncomfortable about flying - than to let a potential victim of abuse elude rescue.

"We encourage anybody, if you see a situation that actually is uncomfortable to you, that you think about that person in the situation who is probably 10 times more uncomfortable, or more," Boeving said.