A piece of cloth to wrap around arm. It is meant to make it easier to recognise friends from foes in the fray of a battlefield or any other chaotic situation.
Added in 0.53, these are intended to be worn as a means of distinguishing members of different groups. Although there is no guarantee that two groups using the same color will not encounter each other, the odds are low given that there are currently seven colors available. The need for identification is particularly important during armed conflict so that friendly fire doesn’t result from the confusion of battle.