Things were so bad these men had resorted to using numbers in communications instead of their names, because if they had been found out early on they would have likely been killed for their troubles.
That's one theory, though the Masons claim their own explanation of the number's significance. For certain, one of the worthies was said to have been John X. Beidler, who being outnumbered by the crooked sheriff Plummer and his rustler and road agent confederates, obtained a small brass mountain howitzer, loaded it with a double charge of powder and a load of printer's type and let fly. Afterward, several locals were observed absent or limping, helpfully identifying the previously masked and unknown criminals.
When it was suggested that Beidler's act was overly brutal, he replied that he was only trying to give the outlaws a chance to better themselves with the opportunity to learn to read.
Beidler was the principal hangman for at least five of the vigilante group's victims, probably including the crooked Sheriff, who was not given a *drop* when hanged but lifted from his feet by the noose so that he'd slowly strangle. The Montana Hangman later survived several narrow escapes in his relentless pursuit of other dangerous men.
"The question of the propriety of establishing a Vigilance Committee depends upon the answers which ought to be given to the following questions: Is it lawful for citizens to slay robbers or murderers, when they catch them; or ought they to wait for policemen where there are none, or put them in penitentiaries not yet erected?"
"Under these circumstances, it becomes an absolute necessity that good, law-abiding, and order-sustaining men should unite for mutual protection, and for the salvation of the community." 
The Bannack gallows where Plummer and his deputies were hung; remarkably, they were ordered constructed by Plummer himself. Photo courtesy of the Bannack State Park.