Stormwind Assassin's Guild
Stormwind Assassin's Guild (or the Stormwind Assassins' Guild and simply the Assassins' Guild) is a group of assassins operating in Stormwind City. Mathias Shaw is either a member or its leader.
Lady Katrana Prestor once sent an assassin of the guild to hunt down the gladiator known as Lo'Gosh. The assassin met with Magatha Grimtotem, who was told by the Forsaken of his arrival. Magatha revealed to him the location of the gladiator Lo'Gosh. Later on the assassin was killed during a fight with Valeera Sanguinar in Dustwallow Marsh; his demise caused by a tarantula who's web he got caught in. He owned an ebon gryphon named Blackklaw.
It is currently unknown whether the guild is another name for SI:7, or its subgroup or another group.
Before the de-canonization of the RPG books, given the fact that the guild operated in Stormwind, it is possible that both, the item and the comic mentions of the guild were originally meant to refer to the Stormwind Assassins which was apparently meant to be the background for the SI:7.
Alternatively, it could be an alternate name for the Assassin's League or its subgroup.