Las Madres de Plaza de Mayo...Every Thursday afternoon the Mothers of the Plaza de Mayo march in memory of their sons and daughters who "disappeared" during the right wing military dictatorship between 1976 and 1983 when democracy was restored. That period in Argentinian history is known as "The Dirty War" (La Guerra Sucia)...tens of thousands of people (mostly university students) were arrested, tortured, and murdered by the dictatorship, sadly often with the collaboration of the Catholic Church. Women who were pregnant were allowed to have their babies. Then they were murdered and the newborns were adopted by military families.
Many were drugged and then dropped from airplanes into the ocean. The Mothers demand complete accounting by the government, and also want to be a constant reminder of those horrible events in the past. They wear white scarves and carry photos of their sons and daughters who were "disappeared". you can see they are quite old now, but continue their protests.
http://en.wikipedia.org/wiki/Mothers_of_the_plaza_de_mayo