Originally Posted by G-BOAC

Welcome to FlyerTalk and the BA Board.

It shows your FF number (and on BA, the tier as well). If you don't have an FF number, it shows your cabin (hence you've seen 'FIRST'). There is also a VIP tag - there was a thread a while back where various 'BP Stubs of the Stars' were being sold in eBay - some showed such an addition under the name. Boy George was one, for example

Premier shows as BA/PREM.... just as with GOLD/SILV/BLUE.