I know two Prems - both have tags but they are "under cover". From my experience travelling with them they are looked after by BA very well, in a way that is both professional and discrete whilst providing appropriate recognition. However their schedules make mine (as a Gold) look tame by comparison so I know that the stuff that BA does for them is much appreciated.

For a contrast you should look at the equivalent AF "Club 2000", whose black tags are much more liberally displayed but as far as I can work out there is minimal recognition over a Platinum Card (I have flown with a couple of Club Deux Mille holders).