Best Western Rewards has a promotion for up to 3,000 bonus airberlin topbonus miles after four stays between September 1 and December 31, 2013.
You need to register for this promotion and link your Best Western & airberlin topbonus accounts that you can do here.
Note that the bonus is staggered based on the number of Best Western stays you have in Germany and Luxembourg during the promotional period.
Conclusion
This is a nice offer for airberlin topbonus members that stay at Best Western branded hotels in Germany and Luxembourg during the promotional period.