MOSCOW — On Saturday, memorial vigils were held across Russia to mark the Day of Commemoration for the Victims of Political Repression. Since the mid-1970s, at dissidents’ behest, prisoners of conscience across the Soviet Union marked Oct. 30 with hunger strikes, while their friends and supporters demonstrated in solidarity — including, at one point, forming a human chain around the KGB building itself. Back then, it was known as Political Prisoner Day.