It's always a good idea to name your signature when you create it. If you don't type a name, Outlook will name the signature "Untitled," and that's not very glamorous, is it? You can give your signature your name, call it "My signature," or choose anything you like. If you intend to create many signatures, you may want to use more descriptive names for them, so that you can keep track of which signature to use. It's easy to know what's in signatures named, "My work signature," "My family e-mail signature," "My soccer buddies signature," and so forth. It's totally up to you.
In this picture, Bobby Moore is creating a plain signature for e-mailing his colleagues, so that's what he'll name it.