The Minnesota Department of Transportation is taking a step to draw travelers' attention to the growing problem of human trafficking and get them to report suspicious activity.

This week the agency charged with overseeing state roads is putting up posters in 41 rest areas across the state that include guidelines on how to recognize signs of human trafficking and potential victims.

The posters feature a woman looking out the back window of a van and the words "I can't escape They took my passport and ID. Help" scrawled on a dusty spare tire cover. "The signs of modern day slavery aren't this easy to see" the message continues. It also encourages travelers to call a toll-free number to report suspicious activity.

The number is 1-888-373-7888.

Human trafficking often involves travel, including the transport of victims from a base of operations to locations of exploitation, MnDOT said.

MnDOT signed a pledge in January to join Transportation Leaders Against Human Trafficking and make fighting human trafficking a priority.

According to the FBI, the Twin Cities is one of the 13 cities in the United States with a high rate of child prostitution, and Minnesota has the third highest number of human trafficking cases in the nation.

"MnDOT's responsibility for maintaining the quality and safety of multiple modes of transportation.. and provide unique opportunities to see and stop human trafficking activities," said Charlie Zelle, the state transportation commissioner.