You can create multiple signatures on the Preferences tab. One of them becomes your normal signature that shows up automatically in your message when you write a new one.
If you would rather use another of your signature when you send a message, go to Options in the message > select Signature.
Send from another persona
Would you like the message to appears coming from a different role than your private, for example from you in the role of answering economic questions, you can create a persona and maybe even a separate signature for.