WASHINGTON -- D.C. is one of the top 15 places in the country for sex trafficking. And you’ve probably walked through one spot where is happens a lot.

Maybe you go to Union Station to catch a bus or a train or maybe a metro train, but did you know that sex traffickers go there to catch their prey?

That’s why a new photography exhibit by ArtWorks for Freedom in the transportation hub’s Grand Hall talks about human trafficking and the signs, so you can help fight it.

RELATED: Sex Trafficking: It's happening right now in DC, & we need your help

Andrea Powell is an advocate with Just Ask Prevention. We asked her what to look for.

"You’re looking for someone who doesn’t know where they are, who looks like they don’t fit in, maybe a young girl or young boy with an older individual, who looks scared, who looks controlled, but not speaking for themselves or an individual who looks like they’re with a group of people and they don’t belong together."

Andrea says the victim could be as young as 8 years old although many are in their teens.

"Maybe it’s a young teenage girl who’s 16 or 17 years old who’s standing around in clothes that doesn’t fit in. Like it’s February and it’s freezing outside and she’s wearing a miniskirt and flip-flops. And she’s looking nervous and looking scared, that individual may not be a victim, but she may be."

Andrea says it’s best not to intervene but rather to call 911 or the National Human Trafficking Hotline at