vigilante; member of a vigilante group
Refers to a person who belongs to a self-appointed group that patrols or enforces order, often in a community context.
Vigilantes are patrolling the streets at night.
He works as a member of the local vigilante group.
自警団 is the vigilante group itself, while 自警団員 refers to an individual member of that group.
Compound of 自警 (self-watch, self-policing) + 団 (group) + 員 (member).