STAMFORD — The birthday of civil rights activist the Rev. Dr. Martin Luther King Jr. took on extra significance this year as the nation’s first black president prepares to leave office and the country braces for a leader who many fear will undo hard-won civil rights advances. Participants in the city’s annual MLK Day rally marched through downtown Monday singing and chanting, holding signs in support of President Barack Obama, who leaves office this week. “The current political climate has made everyone pay attention to everyone’s civil rights,” said Stamford resident Sonya Gleaton, 47. President Obama ends his term the same week the nation celebrated King’s Jan.