Secret Identities and your Magical Self.
On MahouMUSH, Magical Identities are typically kept separate from day-to-day identities, and often a carefully-guarded secret. Luckily, there’s almost always secret places to duck away and transform when you need to. On MahouMUSH, it’s assumed that is what happens when someone transforms, unless they specifically state otherwise in their pose.
It’s possible to not operate with a Secret Identity if that’s the way you wish to do things. Nanoha most certainly has no problems introducing herself in full to her opponents.
Basically, no one may find out who you are behind the mask or magic without your consent. But keep in mind, the moment someone knows who you are, the cat is out of the bag a little, and if that person has a big mouth, more people than you wish might find out who you really are. A Magical Hero should really only share her/his identity with those she/he trusts.