I also have CBA on most of mine.

It can't be Club in the Club World/Europe sense or as in Executive Club, as I hardly ever buy anything other than Y or W and most of my bookings have my QF number in.

However, almost all of my BA paid bookings have a discount of some sort. Either shareholders, or the special £5 discounts that have been appearing recently.

Alternatively, it could just be a reference to an internet booking, as in Customer-Enabled British Airways.