Like all of the other spells in the calm line, they have a chance to resist when cast on a mob. Weather you resist is based on your level, skill, the creature's level, and its magic resistance. If the spell fails, the creature has a chance to not aggro, which is based on your charisma. So increase your charisma if you don't want creatures to aggro on you.
How do you tell which creatures have been pacified? The one you targeted will have it, and the 4 clostest to it will also have it. This spell is extremely useful for pacifying a group of mobs. You can ae mez, ae pacify, and ae memblurr up to 5 mobs at once. This way when they break mez, they will simply walk back to their spawns, and their aggro radii will be reduced with Wake of Tranquility.