This is coolbert:
"There is nothing quite comparable in modern armies to the Roman standards, signa, except perhaps the regimental colours. They performed the function of being a recognition signal and a rallying point. Army units required a device to watch and follow in battle conditions and the soldiers also needed to recognize their own at a glance."
Here, again, thanks to John Keegan/"The Face of Battle", a description of how the Romans would use and employ their standards in battle [rallying point, keeping formation, location of the commander, recognition signal]!
From the narratives ["The Commentaries"] of Julius Caesar himself.
Describing here a Roman combat against the Nervii, B.C. 57:
"The soldiers were crowded too closely together to be able to fight easily, because the standards of the Twelfth legion had been massed in one place. All the centurions of the fourth cohort had been killed, together with its standard-bearer [the most dangerous place on the battlefield] and its standards had been lost. . . . shouting encouragements to the rest [of the Romans] he [Caesar] ordered them to advance the standards and deploy into extended order, so that they could use their swords more easily."
[The Romans standards were too closely bunched. Consequently, the soldiers [of each cohort] found themselves unable to swing their swords freely. The ability of the Roman to fight was severely impeded by bunching of the standards.]
Caesar, single-handedly reorganized the cohorts so they could fight in an effective manner.