I don't think anyone mentioned looking this up in the Microsoft Manual of Style for Technical Publications (or asking a technical editor). Here is the guidance on this:
Use "log on" or "log on to" to refer to creating a use session on a computer or a network. Use "log off" or "log off from" to refer to ending a user session on a computer or a network. Use "sign in" and "sign out" to refer to creating and ending a user session on the Internet. Do not use log in, login, log onto, log off of, logout, sign off, or sign on. Hope this clarifies things. Lea Galanter Lead Technical Editor and Writer Attenex, an F T I company
