From netmanners.com, Dos and Don't of Signature File Use:
#5
DON’T use formatting in your sig file (or your business emails). This includes ASCII formatting, font colors and bolding or including graphic files (which can show as attachments) in lieu of a plain text signature. You are in essence then contributing to the recipient’s attachment folder unnecessarily requiring they have to weed through your signature file graphics to get to the important attachments they were expecting. If you wouldn’t turn your name or title bright red on your company letterhead – don’t do it in email.
