User blog comment:FairyRaven/Fairy Tail Chapter 346: Retrogression Magic, Review and Commentary/@comment-1359064-20130802130317/@comment-7418318-20130802133441

Could it be Pheonix Grave?

The symbol might also be a stylized bird, with the G of Grave and the flames associated with Phenixes.

It's one of those guilds that was only mentioned in connection with the "Wizard I'd Like To Be My Boyfriend" rankings in the weekly sorcerer.