[Austin W Hogan]

Thank you , Richard and Drew, this is the most challenging question and topic that has been on the forum in several months.
First, I think collecting Parker made barrels would be a great niche for a serious collector. There is not a lot of information available and it will take serious study to learn to identify Parker made barrels. There are some beautiful Parker barreled guns; Robin Lewis 16 ga L5 is a prime example, and the L2 twenty gauge of Burchard's, shown at last year's Annual Meeting is another. The Parkers in this period have very nice engraving in all grades, and those with ball grips have the best checking patterns of all Parkers. Among these are some guns that look like the barrels were welded up at the bar at a plumbers convention.
With respect to the direct question I have found the PB in shield on some early guns that were refitted with later barrels ( s/n 1953 is one I can account for); it may have been a repair stamp at that time. The PB in shield re appears just after WWI ; it was used as a proof mark on guns shipped to the British Empire that required proof marks to be imported; Ron Mc Donald has a few of these, as noted in PP a few years ago.
The attached pictures show an L3 , 14056. The number on the flats is the order number. It has been to several PGCA meetings and there is a sort of consensus that it is a Parker laminated barrel. Note, in the first photo the P on the flats, in the spot the barrel steel is usually stamped. The second photo shows the change in pattern at the joint, in agreement with John Davis finding that Parker laminated barrels were made in three segments. The third photo shows the L R pattern difference. This is probably one of the plumber's convention guns, but the checking and engraving are so nice I can't part with it.

Best, Austin