If it is the first time you using SignCut and your usb-option is not showing up it means that either your cutting plotter isn't powered on, recognized by the computer, or you haven't installed the usb-driver. (the driver can be installed from the disk that came with your cutter, or can be downloaded then installed from the resellers/manufacturers website.
If you've had your cutting plotter connected through usb and it has been shown before in the drop down list, but now has disappeared. We recommend that you reset your cutting plotter. (unplug the cable and power the cutter off, then plug the cable back in and power the cutter back on) Then close and reopen the cutter setup dialogue and see if your device/port is in the drop down list. If that doesn't help then connect the usb-cable to another usb-slot and if that isn't working then try another usb-cable.
If it still isn't showing up contact our support or the reseller for further instructions.