"A team of researchers from the University of Pennsylvania had group think of individuals from their own lives and then write and deliver gratitude letters to them.  Participants' happiness levels increased significantly over the following week and remained higher than usual over the next month. Researchers found that writing gratitude letters is one of the strongest ways not only to become happier, but also to stay happier for weeks on end!"

(When Likes Are Not Enough- Tim Bono)

Take 15 minutes to write a letter and mail it to them. Take a picture of the letter/envelope (I'm ok if you hide the text) and upload for documentation.