I had an interesting chat this evening with the glassblower Peter Reynolds on the subject of his pontil stamps. The intriguing design in the stamp on Anne's vase, shown in Reply #2 and #5 is simply a carved pattern in the graphite rod used as a stamp. It has no meaning. He said the stamp was used for a few weeks only in 2007.
The unusual reversed J in the other stamp Ross shows is an attempt to make a monogram incorporating the initials of Peter Reynolds and his assistant Jade Riggins. I'm not sure it was so successful!
He has given up the use of stamps and returned to signing.
Trevor