Dr. Tabor,

After viewing the symbol, I remembered that I have seen its like. The most similar comparison I have yet found is the front of the gold tomb of Charlemagne. (Who I have heard claimed discordance from Christ).

After speaking with my sister, we have also come up with a similarity on St. Mark in the book of Kells, the Black Madonna of Vervieres (sometimes said to be Mary Magdelene) and the back archway in the painting of The Last Supper by Jean-Baptiste de Champaigne.

Also, a Byzantine Archangel relief from the 6th century and the face of the Notre Dame de Bayeux are suspicious, but more of a stretch.

I believe it to be a stylized version of a crown or halo probably created as a sort of family crest. Once you start looking, it will probably be found in many more Christian paintings etc.

Important point, though, was this s Christian symbol when it was placed on the tomb? If so, it would seem to definitely mean this was Christ's tomb, as very few, if any such tombs would be Christian at the time of Christ's death. They would have been simply Jewish, non-Christians.