This is the letter "N" in Arabic. Pronounced "noon" it has been spray painted on houses in Iraq to denote that there are Nasara or Nazarenes living in the dwelling. This symbol has been adopted by Christians worldwide to show our solidarity with our persecuted brothers and sisters, who have been denied what the United Nations has determined to be a universal human right:
"Everyone has the right to freedom of thought, conscience and
religion; this right includes freedom to change his religion or
belief, and freedom, either alone or in community with others and in
public or private, to manifest his religion or belief in teaching,
practice, worship and observance." United Nations Universal Declaration of Human Rights, Article 18.