Show/Hide link in navbar based on userID value

Hi,
I cannot find a way to show/hide ‘log out’ in the nav bar of my _header include file based on the userID (logged in: id>0 / out: id<1). I defined a Security Identity in the Globals so i could access it from anywhere. How can I access my global security identity from the properties panel of the navbar / of the ‘log out’ link?
Thanks