By Anastasia Moloney

BOGOTA, May 5 (Thomson Reuters Foundation) - An old man flanked by young women checks into a hotel, a customer books several rooms on the same floor and no one ever leaves the rooms, another brings guests and walks straight towards the hotel lift without checking in.

These are all possible signs of human trafficking that hotel staff across Mexico City are being trained to spot and report.

An initiative between the Citizens Council of Mexico City, a civil society group, and the Mexico City Hotel Association, which brings together 251 hotels, aims to train at least 2,000 hotel staff this year across the capital.

Staff in at least six, mostly high-end hotels have been trained in trafficking since the initiative started in March, said Luis Wertman, head of the Citizens Council, which provides the training.

"We view the crime of human trafficking as a chain. And every chain is made up of several links. One of the most used links - tools - that traffickers have are hotels," Wertman told the Thomson Reuters Foundation in a phone interview.

"If you have trained people at the reception, at the front desk, the cleaners, housekeeping, anyone that works in the hotel, they can easily recognise when someone is in the hotel against their will."

Read More: Flight Attendant Rescues Human Trafficking Victim With Note Left on Bathroom Mirror

Hotel rooms can be used to film pornography, where women and children are sexually exploited, or a base for traffickers and their victims before victims are sold into sex or forced labour and transported to other parts of Mexico, Wertman said.

In Mexico, and across Latin America, the most common form of human trafficking involves women and girls forced into sex work.

Nearly 380,000 people are trapped in modern slavery in Mexico, according to the 2016 Global Slavery Index by rights group Walk Free Foundation.

Wertman said when hotel staff ask guests questions in the right way, it can help detect possible cases of trafficking.

"Not questions like, 'Are you here against your will?' But more like, 'Excuse me sir, what's the relationship between you and the guest,'" he said.

"From those quick questions and answers you can notice when something is not right."

Hotel staff send confidential reports of suspected trafficking to the Citizens Council, which then passes them on to "trusted" authorities, including police and prosecutors, who follow-up and investigate, Wertman said.

"Can you trust every authority?. In our experience, the answer will be no. Are there trusted authorities? The answer is yes," he said.

Mexico's 2012 anti-trafficking law punishes those convicted of the crime to up to 40 years in prison.

Eloy Rodriguez, head of the Mexico City Hotel Association, said hoteliers have a role to play in combating modern slavery.

"Hotels are open to the public and as such are vulnerable, Rodriguez said. "Bad people and criminals use hotels and being part of this initiative is one way to prevent trafficking."

The next initiative is to place bottle neck tags, with an anti-trafficking hotline number, on 30,000 bottles of water in hotel rooms across Mexico City, he said.

(Reporting by Anastasia Moloney @anastasiabogota, Editing by Ros Russell.; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights, climate change and resilience. Visit http://news.trust.org)