welcome!
Are you not doing a contour cut? If you are, the cut line would be cut off, so I assume you are just printing.
If you are printing in Omega & not needing to cut, in the GspPlot program, you can click on the 123 icon & you will see your foil colors listed. The color that is designated to print a target will have a "T" after it. If you click once on the name of the color, the "T" will go away & no target will be printed.
However, if you require a specific amount of blank unprinted vinyl to remain outside of your print... & you don't want to risk forgetting to advance the material between multiple prints... you could put a cut line right where you want to cut the print... even if you intend to cut it by hand... by adding it to the file, the "target" (registration mark) will fall outside of that line... so put it as far away from the print that you want to have clear unprinted vinyl...