The Intuit Small Business Blog published Use Your Email Signature to Grow Your Business, discussing what to put in and keep out of your email signature.
Some people get carried away “accessorizing” their email signatures. Avoid images (such as photos of yourself or your product); many email systems automatically strip these away, anyway or turn them into oddball attachments.
While were on the topic of email, The Art of the E-Mail Subject Line via Business Week is worth taking a look at.