Mine means Mud Doctor. I work in the oilfield, and I used to work on the rigs as a mud engineer. We are often referred to as the mud doctors on the rig. I just shortened it, and have been using this name on forums and games since about 1997.

I also have one other user name that I use on occasion (although I don't remember ever using it on a reptile related web spot), and that is sgt6114. That is short for Sargeant -my rank in the USMC and 6114 which was my MOS (flight line helicopter mechanic on Hueys and Cobras).