A few years ago, on board a flight from Los Angeles to New York, a group of young girls wore nothing but jeans and T-shirts — in the middle of winter. They didn’t speak English, and they didn't speak to each other the entire flight. I remember thinking it was odd, but I didn't know what to do about it.

My mother, a retired flight attendant, once had a man on board a flight traveling with a teenage girl. They didn’t look like they were related, and they weren’t friendly with each other either.

“When I asked the girl what she’d like to drink, he answered for her," my mother said. "I thought that was weird since they weren’t speaking to each other. If I'd known more about human trafficking, I might have engaged them in conversation to feel the situation out, but at that time we didn't know anything about it."

Back then human trafficking never crossed our minds. But that has changed.

At a funeral service. Look what I found in the pew. A sign from God? pic.twitter.com/XZu7ufIyRz — Heather Poole (@Heather_Poole) January 5, 2016

A few years ago, my airline started training us on spotting telltale signs of human trafficking on the plane. Can the passenger speak for themselves, or is someone with them controlling what they say? Does the passenger avoid eye contact? Do they appear fearful, anxious, tense, depressed, nervous, submissive? Are they dressed inappropriately, or do they have few possessions — even on a long flight? Can the passenger move independently, or are they accompanied by someone seemingly controlling their every movement?

My colleagues and I have learned this because of an American Airlines flight attendant named Sandra Fiorini. She testified before Congress about what she'd seen on one of her flights, and how she hadn't known what to do about it.

When she saw an 18-year-old boy on a six-hour flight carrying a newborn — with its umbilical cord still attached — with a single bottle of milk and two diapers in his coat pocket, she had tried to report it, but she couldn't find anyone to help. That’s when she realized something needed to be done.

Fiorini joined forces with Deborah Sigmund, founder of a nonprofit organization that fights child exploitation and human trafficking, to educate airline employees and create a human trafficking hotline. Airlines employees are the first line of defense for protecting the countless children who are trafficked on major flights each day.

The State Department estimates 2 million women and children are victims of human trafficking every year. There are more slaves today than any other time in human history: Human trafficking is one of the fastest growing crimes in the world, second only to drug trafficking. And while drugs can be sold once, a person can be sold several times a day. It’s a business that brings in an estimated $150 billion every year.

Thanks to a flight attendant we now have a human trafficking hotline. 1-888-373-7888. Check out @InnocentsatRisk https://t.co/hHKG8V691c — Heather Poole (@Heather_Poole) January 5, 2016

Did you know the Super Bowl, like many large events, sees an uptick in human trafficking? That victims will be brought to the Bay Area, where the event will be held this year, to be sold over and over again to men at the game? Since flight attendants have been trained on how spot it, we're asked to volunteer to help police at the Super Bowl each year, and every year people get arrested for human trafficking. Not just prostitution, but human trafficking. Think about that while you’re eating chips and dip, enjoying America's favorite past time with your friends.

Even though I’d been trained on what to spot on the aircraft, I never thought about what happened to these people on the ground. For me, it ended when passengers walked off the plane. Because I didn't think I went to places where things like that happen. Because I didn't think I lived somewhere where, you know, people sell other people.

But as it turns out, I was wrong. It happens everywhere, in strip malls across America

I live in Redondo Beach, where most people at town meetings are more concerned about beautifying the waterfront than anything else. It wasn’t until a few years ago, when I met a woman at my son’s swimming lesson, that my eyes started to open.

When she heard I was a flight attendant, she asked about our human trafficking program. She belonged to a local nonprofit group involved in helping victims of human trafficking, and it was during this chance encounter while our sons swam laps that she told me about a massage parlor a block away that her group was watching. A block from the pool — and about five blocks from my house. A year later the police busted the place for prostitution and they closed shop, only to be replaced by a few new places down the street. One step forward, three steps back.

Yesterday I pointed out all the massage parlors on Artesia Boulevard to my mother in law. She said I was giving her whiplash. #RedondoBeach — Heather Poole (@Heather_Poole) January 12, 2016

Redondo Beach is a very nice town — a very nice town with way too many massage parlors. A Yelp search for massage brings up 88 results in a town covering six square miles.

“One in every strip mall,” she said that day at the pool. That’s when I started to do my own research, and how I found myself standing before the city council in November.

See also: New campaign matches Tinder users with sex trafficking victims

I’m not a public speaker — unless you consider telling 165 people how to use their oxygen masks to be public speaking — but there I was with three minutes to tell them everything I knew, to try to open their eyes to a real problem.

That night it was a packed house. Most of the people there were wearing matching T-shirts to show the council members they meant business: They were there to discuss beautifying the waterfront. I guess when you live in a beach town and spend most of your time facing the ocean, listening to waves crash and watching beautiful sunsets, it's easy to miss what’s going on right behind you. Only two of us were there to speak out against the massage parlors.

"California Beach City Enlists Private Partner to Rejuvenate Pier" by LAUREN HERSTIK via N… https://t.co/EbNHSpNar6 pic.twitter.com/fknKXHG562 — Money Channel NY (@moneychannelnyc) January 12, 2016

After I introduced myself I told everyone I was a flight attendant for a major U.S. carrier. Truth be told, it was the first time in my life my job actually made me feel like I knew something important. It felt like an episode of Parks and Recreation. Here I was, this blonde who came out of nowhere to discuss something that sounded outrageous.

I started with the signs of a fake massage parlor: Security cameras outside, customers getting buzzed in. Windows covered with bars, boards or dark curtains, employees who rarely leave the location.

I shared facts, I told them the warning sings, I even shared a story about a neighbor who had called one of these places to schedule a massage. The woman who answered the phone asked if the massage was for her husband. When she said no, the woman on the other end of the phone laughed. Another time, my neighbor asked her manicurist at her favorite nail salon about the foot massage place next door. She told her not to go there — because only men go there.

After my three minutes was up, the city council said they’d look into it. Maybe they will ... after they’re done beautifying the waterfront.

When I talk to friends about the number of massage places in town, they look confused. “What massage parlors?” they ask me. When I mention human trafficking they look at me like I'm crazy. "How can that happen here?"

Easy. It starts with massage parlors.

Some of my friends drive their children to school down a street where there are 13 massage parlors in the span of two miles. On this same street, the grocery store went out of business, the dentist closed up shop, but all the massage parlors that nobody seems to notice are thriving. Prostitution is one thing — after all, it’s theoretically happening between two consenting adults — but there could be something darker happening here. I don’t care if somebody wants a happy ending. But I do care if somebody forced into captivity is the person giving it to you.

We're talking about a beach town not far from the Los Angeles airport, where the median household income is almost $100,000 and the median household value is a little over $700,000. In 2012, my town was named one of the top “best places for the rich and single” by Money Magazine. This is not the kind of place where one would imagine human trafficking to occur — but that may be exactly why it continues.

These places set up shop in the middle of a strip mall, right in front of everyone’s eyes, making it easy to assume something like that wouldn’t be happening. It's in plain sight. How could something like that happen in a strip mall near a dance studio for children? I could show you a place. Right next to an ice cream store.

Oh, I'm sure most of the 88 massage places in my town are on the up and up, but you can't tell me all of them are. You can't tell me we shouldn't take a closer look. But if the community doesn’t know what to look for or doesn’t believe it can happen "here," nothing will change. Knowing what to look for is the first step to stopping modern day slavery.

Next time you see a shady looking massage place, notice if the entrance is uninviting, or security cameras are pointing at the door. If the windows are covered with metal bars, ask yourself if the bars are there to keep people out — or to keep them in?

Still with me? Here’s one of the best articles I’ve read about human trafficking. It focuses on massage parlors and explains what to look for and why it’s so hard to stop. Please, I beg you, read it. You’ll never look at a strip mall the same way again.

Heather Poole is a flight attendant for a major U.S. carrier, and the author of the New York Times bestseller Cruising Attitude: Tales of Crashpads, Crew Drama and Crazy Passengers at 35,000 Feet. You can follow her on Twitter at @Heather_Poole.