I had some custom graphics put on a spinnaker, they told me they use a projector to put the image onto the sail and then hand paint it on, and it ain't cheap! About $600 for one spinnaker, only using two colors. Don't use tape, it will come right off when the sail stretches with the wind. The majic marker might work the best if you want cheap and simple. You could hand paint it on if you can find out what type of paint they use. Contact your sail maker, he will know.