lets say your account/site name is "Dudebro" then you make a character named "MLGsinper"
when people look at guild/friends list they will see "MLGsniper (dudebro.1234), the numbers are random and everyone gets them added to their names. this way you only add the person once, then you'll see them online no matter the character they pick/make
From my experience, people running around /saying will use your character name, of course. But in our guild, especially if someone swaps alts often, it is easier to just address members by their account name.