I have seen many solutions used. Laminated name cards, cut plastic bottles and the always excellent beer can aluminum, preferably the really light ones. Cutting off the grit coming into the BB is all that's needed.

Key suggestion: the cut beer can is among the very best solution, because you can scratch your name and phone # on it. This can be useful.

I recently opened up my '71 TdF that had been in deep storage a few (too many) years, and found a faded beer can sleeve with my name and parent's address on it. The BB was in fine condition, too.

w/re to the cheap plastic sleeves: If you've got an order sufficient to be worth the huge S&H fees attached, stock up. You can still use the beer can I.D. sleeve, too.