In some ways you can tell if a person is a FF by just looking at them, tag or no tag. If you see an unaccompanied young-un or backpacker it's often an A3 Gold.
Much the same way you can spot if a person has just gotten his status by his way of acting over entitled (like OP for instance, expecting free upgrades as FTL) or by constantly flashing their cards.
now I finally understand why so many SENs (or not sens) walk around with their SEN luggage tag - they learn it from the LH marketing ^
It could also be due to the fact that the SEN tags are so discrete. Only a trained eye will recognize them whereas the infidel will have no way of telling. This as opposed to other Gold/Platinum bling bling tags whose sole purpose is to attract attention.