armband
n.a piece of cloth or plastic worn around the upper arm. It is often used to show a person's role in a group, like a leader or a referee.
n.a strip of fabric or plastic worn around the upper arm, typically to indicate a person's status, role, or team affiliation.
“The referee wore a bright yellow armband to show his position.”
“The team captain was easily identified by the red armband he wore during the championship match.”
“In many professional leagues, the captain is distinguished by a black armband, a tradition that serves both as a visual identifier and a mark of leadership.”
“I would arrive armed with what I liked to call my anti-drowning armour: armbands, floats, goggles, and a swimming hat.”
“Now wearing the captain’s armband, he scored twice and set up another as Dino Toppmöller got off to a roaring start as Lens manager .”
From arm + band.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.