Watford Amnesty Group ran a stall in the Intu Shopping Centre, offering people the chance to correspond with victims of human rights abuse.
The event took place on Sunday (January 12) outside the Disney Store, from 11am to 5pm.
Shoppers could fill out a card with a positive message, which was then sent to an individual or family suffering around the world.
Mark Nicholas, from Watford Amnesty International Group, said: "Receiving a greetings card from someone hundreds of miles away can make a tremendous difference, just knowing that people are thinking of you and care about you.
"Cards can also give hope of families whose relatives have disappeared and to people in danger because they are defending human rights."
Mr Nicholas said the cards are also used as a form of petition, to publicise the plight of some of the world's sufferers of human rights violations.