The Ning ID authentication system lets you choose an email address and password once and use it to join or sign into any social network that uses the Ning ID.
When you create a Ning ID, you can also add a set of basic details and your photo to your Ning ID account. These details are then pre-populated whenever you join a new social network that uses the Ning ID for authentication. It also enables you to keep track of your friends and messages across all the social networks that use it.
You can sign in with your Ning ID email address and password whenever you see this symbol: