You can rub a marker around the circumference of your field point to help differentiate between the two ends of the arrow. A little bit of marker ink will get transferred to the paper as the arrow passes through. After you do it a few times, you’ll be able to tell which end is which without the marker.
Edit: I bumped my rest over and shot a couple bareshafts through paper tonight to create a nock right tear and give you an idea what a bareshaft looks like through paper. The point end of the tear is more defined and the nock end is more ragged. On the upper shot I rubbed some black Sharpie on the field point and you can see some ink streaks left on the paper.
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Shoot an arrow through paper. Retrieve that arrow, rotate the nock 120°, shoot that arrow through paper again. Retrieve, rotate nock another 120°, shoot one more time. Now compare the 3 paper tears and leave the nock in whatever orientation gave the best looking tear.
This assumes a 3-fletched arrow; if you're shooting 4-fletch, you'll rotate the nock 90° at a time and have 4 tears to compare.