Sin was a good name for Jericho's guild. In a single word it conveyed so much. Immorality, perversion, offensiveness. Most importantly, it conveyed that his very existence was an affront to the established power. Which is why joining Sin resulted in being placed on the kill on sight lists of three of the largest guilds in the game. It made recruitment difficult.
Fortunately, Jericho was still the number one mage in the game and his fame went a long way. On top of that, his alliance with Tiamat ...