Another point, go to settings, Labs, and enable Canned Responses.
This enables you to create multiple different signatures to use on different occasions - depending who you are sending it to. As you are typing the email, with one click you can pop in a pre-written signature.
You can have one for family, one for business, etc.
Once you are in Labs, enable "Undo Send" which gives you a few seconds after you click 'send' to retract the email! VEEERY useful because you usually remember what you left out of the email a second after you press send!!