The Flags:

Organized out of the chaos of Armageddon, The flag army instills fear among all those that encounter their numbers.
At first the group began with just three of Gareth’s former employees, people that did not necessarily like Gareth but found in him a strength they could not muster alone. These three employees brought with them their families and the group was immediately approaching 12 members upon its inception.

Gareth’s ambition to lead people was enough to rally virtually every man woman and child he came across to join his cause, and those that refused him were rallied up and shot as sympathizers to the Reapers ideals, their personal items, food and water integrated into the group. He and his army would preach against all that the Reaper stood for and work to re create the world they knew.

The flags emphasis on hate towards the Grimm Reapers ideals and his final act upon the world was a very powerful message and one which few would disagree with. Thus their purpose was clear and their membership ever on the rise.
Gareth’s vision of leading had been realized without a vote and without resistance.

The flags soon acquired a symbol, one which the Reaper wanted to oppress, but one he embraced when carrying out his final act. This symbol would represent all that the Reaper wished away. This is how they were known to Joel and his friends as the flags