Found on Twitter, Google is currently testing a new extension featuring promo code as a brand new extension. Shown here from Williams-Sonoma, Dr. Pete found this while searching. The promotion in question was an offer for 20% off your entire order and used text to indicate the promo code offer to use.

Currently, Google offers several ad extensions for advertisers to use with their ad copy. Shown below, the image included Ratings, the new offer/promo code extension, Sitelinks & the Location extension. Right now, I do not know of the name of the ad extension itself.

all extensions options 1