Personally, if I need to convey to someone that they aren’t dealing with some yahoo, particularly if I think they need re-assurance that someone in a position of responsibility has given deep thought to whatever they requested or need, I stick in my Ph.D. after my name. I have to field a lot of irritable e-mails from people in response to their complaints about our pan-governmental employee surveys, or suggestions for improving it. In those cases, I always respond as Mark Hammer, Ph.D., because they deserve to think they are being taken seriously by someone closely connected to the survey design. Most of the time, though, I’m just “Mark”, and omit any signature, whether I’m responding to someone higher up or lower in our corporate chain of command. It’s just a credential that determines my pay, and little else.