Sign software is probably a bit easier in that all you have to do is output the vector artwork to a plotter & away it goes, what software are you using & what files are you being sent? Has the supplier sent you a gcode file for you to run on mach3 or has he sent you a vector file for you to produce your own toolpaths from?

If you open mach3 can you move all 3 axis alright & have you tried inputting some gcode commands directly to see what happens rather than opening a saved file.