@Misty29 @Ben551
While it's not available on AirBnB we found it very easy to do.
We have had business cards printed up with our details plust a 15% discount (which is roughly the upper end of the AirBnB commission plus booking fee) for anyone contacting us again - on the card it says 'Quote 'xxxxx' when contacting us for a 15% discount on your next stay.
We put them in the bedroom on the hospitality tray and let guests know they can take them for friends or family.
If they book via the site then we adjust the price after booking to reflect the reduction. If it's friends and family they tend to book direct anyway because they know us.
As for our own friends and family, it was a quick email with info for their friends or families.