There are situations when you want to switch to another signature while writing a message. For example, your formal signature with business contact information may be the one you assign to your work e-mail for corresponding with customers. When you are just e-mailing co-workers that know you, you probably want to use a less formal signature.
Switching to another signature in a message you are composing is easy, if you are using Word as your e-mail editor. You would right-click anywhere in the signature, and then choose another signature from the menu that appears. Every signature you have created and stored will appear in that menu.
If you are using Outlook as your e-mail editor, you would select and delete the signature in the message and then use the Insert menu to pick another signature. That's pretty easy too.