Signum
Each century had its own standard, called a signum.
Standard Bearers in the Roman Army
Caerleon Net
Vexillum
When a detachment was sent out they took a vexillum, a flag type standard. This showed which Legion they belonged to.
Cornicen
Standards helped the troops to keep in the right positions during battle. The cornicen also gave commands by sounding different signals on his large circular horn.
Aquila
The aquila, a golden eagle was the standard for the legion. This only left camp when the whole legion set out.
Imago
The Legion carried a portrait of the emperor, the imago, this was to remind the troops they owed their loyalty to him.
Video clip showing standard bearers