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. It comprised a number of philarae (disks or medallions) along with a number of other elements mounted on a pole. The pole could be topped with a leaf-shaped spear head or a manus (open human hand) image denoting the oath of loyalty taken by the soldiers. It sometimes included a representation of a wreath, probably denoting an honour or award.
The task of carrying the signum in battle was dangerous as the soldier had to stand in the first rank and could carry only a small buckler. It was this banner that the men from each individual century would rally around. A soldier could also gain the position of discentes signiferorum, or standard bearer in training.