You mean what if someone uses a faction tag while not being part of the faction? Seems obvious, the player does as he wants and the faction gets the blame.
//edit: Or credit.
I have a feeling theat the whole thing about factions claiming to be representative of an entire faction within the game is going to come up. But if someone uses a tag that a group of players use to mark their collective identity wihtout permission that's kind of like impersonating someone.