[Researcher]

I think the only exception to this would be Parker Special Steel which just had the PS stamp with no circle.

From my observations I find the early Parked Spec. Steel barrels being marked P.S. on the barrel flat.

191194 04 P.S. barrel steel.jpg

Beginning in the 204xxx range the handful of GH/GHEs I've recorded have the PS in a circle --

204493 05 LNN3, L= February, NN = 1944; PNN3, P = June, NN = 1944; PPP3, P = June, PP = 1945;.jpg

221144 03.jpg

223261 02.jpg

231691 03.jpg