"a group of self-appointed vigilantes" It is literally the defining concept of vigilantes that they are self-appointed!
It is literally the defining concept of vigilantes that they are self-appointed!
Well, they could be appointed by Committees of Vigilance, which were themselves self-appointed, like the Committee of Public Safety which claimed authority from the people in the French Revolution, which recall was an inspiration in living memory for much of the 19th century apex of American vigilantism (the Southern color line wasn’t the only thing being enforced by mobs and lynch law)