[yarou]

I guess it depends on whether or not you want your code to read like natural language.

The refactored version reads like:

Allow access to the site if the user is signed in or has a trusted IP.

The original (DeMorgan's applied):

Allow access to the site if the user isn't signed out or doesn't have an untrusted IP.

It does help to have a good understanding of propositional logic and Boolean algebra, though.