Answer: watermarks

AnswerCrossword Clue
WATERMARKSIdentifiers, of a kind
WATERMARKSPaper impressions
WATERMARKSStationery impressions
WATERMARKSPhilatelist's concerns.
watermarksA faint design made in some paper during manufacture, that is visible when held against the light and typically identifies the maker
watermarksWATERMARK, to mark with a watermark