From the Gratitude Campaign Website:

http://www.gratitudecampaign.org/index.php

A quote from the website author:

"For the past several years as I've been traveling around the country, I've been approaching soldiers in the airports and thanking them for serving for us. On several occasions I have noticed that it felt a little awkward for both of us. There are several reasons, some of which I am even just now learning as I produce this film and talk to more soldiers. But they have always appreciated being thanked, and I have always felt better having expressed my gratitude.
I started to think that it would be nice if civilians had a gesture or sign that they could use to say "thank you" quickly and easily without even having to approach. I did some research and found the sign that we are now using.
Is this limited to the military? Not at all. If you look around you I'm sure that you'll find lots of people who are serving their communities, from local to global. If you appreciate their service, give them a sign. Say "thank you.""