Rolling Thunder, a national nonprofit organization dedicated to prisoners of war and those missing in action and their families, has asked Dedham to participate in the group’s program of putting out empty chairs to honor lost members of the armed services. Dedham selectmen unanimously agreed at a meeting on Jan. 16. Since World War I, there have been nearly 92,000 missing POWs, according to Rolling Thunder President Joe D’Entremont. “That’s a lot of families that don’t have closure,” he said at the meeting. An American flag will be posted with the chair, along with a plaque dedicating it to the missing serviceman. Selectman James MacDonald said an empty chair is a powerful symbol. “It’s something that brings awareness, and I commend you for bringing that to Dedham,” MacDonald said at the meeting.