BALTIMORE (WJZ) — A number of Uber drivers in Baltimore took part in a training Tuesday designed to help them spot possible signs of human trafficking.

The ride-sharing service partnered with the Polaris Project, a non-profit that fights human trafficking and runs a national hotline, to teach drivers about the warning signs a victim may show.

READ MORE: First Alert Forecast: Severe Thunderstorms May Move Into The Area Monday

Among the possible red flags:

  • A customer asking to be dropped off at a hidden entrance
  • A customer trying to pay with cash from a large stack of bills
  • A potential trafficker exhibiting control over a victim
  • Signs of physical or emotional abuse
READ MORE: Van Hollen Suffered Minor Stroke In Western Maryland Over The Weekend

Polaris said there were more than 650 sex trafficking cases reported to their hotline in Maryland between December 2007 and June 2018.

Uber has also put information on its website for drivers who couldn’t make Tuesday’s training.

MORE NEWS: Up To $16K Reward Offered For Tips About Murder Of East Baltimore Pregnant Woman And Fiancé

Anyone who suspects they have information about possible human trafficking should call the National Human Trafficking Hotline at 1-888-373-7888 or text “Help” to 233733.