The principal of the Islamic School of Rhode Island said he is taking extra precautions since the school was tagged with offensive graffiti, but that life there is returning to normal. The FBI is conducting a civil rights investigation into the vandalism at the West Warwick school on Feb. 14. The entrance was tagged with graffiti that read ‘‘Now this is a hate crime,’’ “pigs,’’ and offensive references to Mohammed. Monday was the students’ first day back from February vacation. Principal Abdelnasser Hussein said police officers were there to make sure it went well. Hussein said nearly all of the students attended classes.