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.
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.