Have found no mark for W Fifield !! Found several references to him but no record of his work !! Since he was the person that painted the pot and not the maker,, this does not surprise me !! I did find two other people that were looking for the same mark !! So we know he painted more than one !! Your mark does not look like a factory stamp so I don`t think it was done in a factory, but rather written on by the painter !! Will look more but so far its a dead end !!