AC always used to ask for my BD card, in many places around the world noone know what BD was, including several US airports, and always asked for the card.

There were reports here a while ago that in US lounges people used to get in with golden BD luggage tags because an agent had never seen an actual BD card in their life...

Its easier with UA now (I guess they are a more recognizable member of Star), but AC always asks for the physical card.