A campaign urging people to be more aware of human trafficking will be formally launched later.
The campaign message is being carried on posters and DVDs
The Blue Blindfold initiative, named after images on campaign posters, will be welcomed by MPs and peers at an event at the House of Commons.
The UK Human Trafficking Centre (UKHTC) says the crime often goes unnoticed and wants people to be aware of what is happening in their communities.
The centre has put the key victim signs to look out for on a new website.
These include uncertainty or timidity, loss of freedom at work, loss of personal freedom, physical injury and poor living conditions.
The campaign started before Christmas and posters have already been displayed on buses across the UK.
The message will also be put across through DVDs, postcards and factsheets.
The Blue Blindfold campaign is targeted at four groups - law enforcement bodies, the general public, other agencies and victims.
Nick Kinsella, head of the UKHTC, said a combination of the seriousness of the crime and the hold traffickers have over their victims means it is not visible to the public.
He said: "This is criminals selling people in the same way that they sell any other commodity.
"With people there's an inexhaustible supply and there's good money to be made. If the traffickers are caught they will go to prison for a long time."
Mr Kinsella said victims do not necessarily have to be kept under lock and key to be under the control of the traffickers.
"It's just as an effective method of control to know that a victim has a sister back home and tell them that she will be next," he said.
Mr Kinsella added: "I don't think it's possible to explain the trauma a victim of trafficking goes through. You're frankly treated as a modern day slave."
Anthony Steen, chairman of the MPs' All-Party Group on Trafficking, welcomed the campaign.
He said: "Congratulations to the UKHTC on their splendid initiative which will create greater awareness of modern-day slavery using contemporary and eye-catching advertising."