noun
armband; brassard
A cloth band worn around the upper arm, often to show affiliation, role, or rank (e.g., by security, event staff, or military personnel).
警備員は腕章を付けている。
The security guard is wearing an armband.
イベントスタッフは全員、青い腕章を着用していた。
All the event staff were wearing blue armbands.