A signifer was a standard bearer of the Roman legions. He carried a signum (standard) for a cohort or century. Each century had a signifer (thus, there were 59 in a legion) and within each cohort the first century's signifer would be the senior. The signum he carried was the military emblem of that unit.
A first century signifer. His armour and helmet are covered in a wolf skin and he also carries a small circular shield. The signifer takes his name from the type of standard he carries, the signum. The signum was used as the standard for each maniple in the legion (a maniple consisted of two centuries).