I think the previous comment is right on the money. What is the point of these cards? If you're just handing them out to friends or people that you meet at conferences, simply listing your department and university affiliation should be enough. If you feel like appending a different terminal degree to your name, that might also be appropriate. "John Jay, MBA" or "George Washington, M.Phil." may be appropriate. If you currently teach at a university as part of your graduate studies, perhaps you can list yourself as an "instructor". If it's for a nonacademic job, you can always try "mathematical consultant".

Dov :-)