I usually lay the arrow on the table,cock feather up and nock horizontal and then align the broadhead-no glue.I then mark the footing behind the blade,so I can get it back to that position if it should move.I do like the nail tip idea.
After gluing I want to press it point down to seat the broadhead and insert and then it goes on the tip alignment jig to assure that the tip is centered.With this moving of the arrow,my reference mark helps me make sure that my broadhead is still aligned horizontally.
I also mark my fletching jig so that I can refletch an arrow and THAT broadhead will still be oriented the same,in relation to the nock and fletch.