Google have recently updated their email systems to support rich text email signatures. This means that users of Google Apps (web interface) and Google Mail are no longer stuck with plain email signatures like this:

instead they can include colours, different style text and photos/logos.

To edit your signature:-

1. Log into the web interface for your Google Apps or Google Mail accounts
2. Click [Settings] in the top right hand corner of the screen.
3. Half way down the screen is the option to add a signature, check the Signature Check radio button and enter your details in the box below, making use of the various tool buttons (like a version of Word) to edit the signature you’d like to appear under your emails. (see below)
4. When you are happy, scroll to the bottom of the page and click [Save Changes] – you are good to go!