The Power (or Lack Thereof) of Symbolic Acts

Been thinking about symbolic acts lately and on Thanksgiving it seems appropriate to discuss. TheWife was reading an article that urged the President-Elect to take a large swath of the White House lawn and make it into an organic orchard as a symbol of commitment to sustainability. A number of my students have been fasting to bring attention to world hunger and injustice. I'm wondering about the function of such acts. The fact that I slept on and off in a cardboard box at the University of Maryland for a week most likely is not to be listed anywhere among the active factors that brought down the Apartheid government of South Africa. So, what, if anything, do such acts do? Are they for those acting, to give a sense of solidarity? Is it to make us think we are doing something to help alleviate our feelings of powerlessness in the face of deep, on-going injustice, the real causes of which are political and sociological and so much bigger than anything a well-intentioned individual can help overturn? Is it part of a PR campaign, that we are trying to get a movement started because while a few folks cannot do anything substantive, a large public outcry could?