One of the downsides to a default email signature is that you have to manually change it each time. Give yourself a little more flexibility with canned responses instead.
As tech tips blog Guiding Tech points out, you can create multiple canned responses (enabled via Labs, if you haven't already) to replace your regular signatures. You can still send the rest of your message as usual, then choose the signature you want at the end. This is particularly helpful for distinguishing between professional and personal email.
How to Quickly Switch Between Email Signatures in Gmail [Guiding Tech]