The AxiDraw Drawing Machine (Legacy version)[This documentation is for the older-model AxiDraw, sold prior to February 2016 with white Delrin chassis. Click here for current model support.]
Tracing signatures (12/15/14)
Drawing signatures is a great use for the AxiDraw. However, you need to have a single-line path for the pen to follow. The simplest way of creating this is to manually draw over a scanned signature in either Inkscape itself, or whatever CAD program you like to use. My own favourite is Rhinoceros (http://www.rhino3d.com/).
I place the scanned signature as a background bitmap (View -> Background bitmap -> Place) and then drawn lines using the "Curve: Interpolate Points" tool. Once the curve is drawn, it's exported as an AI file to Illustrator, then saved as an SVG file which Inkscape can open (Rhino is supposed to export SVG files directly, but I can't get it to work).
Here's a screenshot of the signature in Rhino with the traced line on top. The inset shows the line thickened up in Illustrator. Since it's a signature, it doesn't have to follow the original too precisely.