Global Handle
From SFWiki
Global Handles
A Global Handle is a universal username that allows a player to communicate with another irrespective of which character, side, or server they are playing on. Global Handles are prefixed by an @ (at) symbol and by default are the name of the first character that player created and logged in to the game with, although they can be changed later. You can only change your Global Handle a limited number of times.
For a list of guild member Global Handles see the main CoX page: City of Heroes