Having two hyacinth vases with this now famous signature, I've always followed this topic with interest.
Yesterday I picked up a book called An Illustrated Dictionary of Glass by Harold Newman. Coming to the letter P, I found the following:
" PF (or PP) glassware.
Opaque white glassware enamelled by an unidentified hand (one piece is initialled 'PF' or 'PP'), featuring floral bouquets, and also peacocks and CHINOISERIES on a 'floating raft'. It has been said that the decorator was possibly from Newcastle, and that his work has been erroneously attributed to Michael Edkins.
See R.J. Charleston, 'A painter of Opaque-white glass,' Glass notes, Arthur Churchill, Ltd, 13 (1953) p.13."
With my two vases the PF makes sense, remains the letter K. PP I have never seen.
Both my vases are white opaque with very skillfully painted bouquets, that makes sense too.
I bought my vases in England, for what it's worth.
I have no idea about the time frame of any of this, just thought it might give a new outlook on the whole mystery.
Patricia