As a valued AIR MILES® Collector, earn 100 Bonus AIR MILES® reward miles* when you join HHonors and complete a stay at any hotel within the Hilton Portfolio by May 31, 2015.
As an HHonors member, you earn Points on every stay that can be redeemed for free nights and more. You can even earn AIR MILES reward miles on every hotel stay. After you join, just set your My Way™ Earning Style Option to Points & Miles™ in the Preferences section of your HHonors profile and select AIR MILES as your preferred Airline Partner.
Here is a link to the promotion.