The internationally recognized date comes from the Hebrew calendar and corresponds to the 27th day of Nisan on that calendar. It marks the anniversary of the Warsaw ghetto uprising. In Hebrew, Holocaust Remembrance Day is called Yom Hashoah. (from http://www.ushmm.org/remembrance/)
Almighty God, we remember before you this day those killed during the Holocaust, for the innocents murdered, for those who wrongly used your name to kill, and for those who did not speak up against such injustice. Guide us in our efforts to root out intolerance and prejudice in our world, that we may not make peace with oppression and may stand as witness to those who died. Help us to work towards the day when no one will fall to such a sword. We ask this through him who was executed as a criminal by an oppressive state, Jesus Christ our Redeemer. Amen.