What does happiness look like? It looks like Macy, a 4-year-old pit bull in California, and five other faces that have been chosen to represent the International Day of Happiness.

She may seem like an unlikely candidate for such an honor, but Macy has every reason to be happy.

After being deemed "unsuitable for adoption," Macy was rescued from a shelter by Grateful Dogs Rescue, a San Francisco organization that cares for dogs at risk of euthanasia.

Jackie Shen (pictured right), the woman that fostered Macy, fell in love with the dog and decided to adopt her.

Jackie Shen and Macy"I had never considered myself a pit bull person, and if I were honest, they scared me a little," Shen said. "However, Macy completely blew my stereotypes and preconceptions out of the water. The thing Macy loves above all else is human interaction and attention."

Now the pit bull is sharing her happiness with the world, with her face gracing one of six stamps created by the United Nations Postal Administration, as well as the cover of a promotional brochure.

The U.N. established the International Day of Happiness in 2012, and the holiday is celebrated worldwide on March 20.

The photo of Macy that will appear on the postage stamps was taken by MNN writer and photographer Jaymi Heimbuch, who snapped the picture as a volunteer for Hearts Speak, an organization that promotes adoptable dogs. (You can see more photos of Macy on Flickr.)

Heimbuch uploaded her photos to a stock photography website, where the postal administration purchased it.

"Everyone who knows Macy is really stoked,” Heimbuch said. "It's not every day a pit bull gets such an honor."

Shen echoes that sentiment and urges people to look past pit bull stereotypes.

"The main takeaway is, please everyone, just give them a chance — pitties and other shelter dogs alike. That's really all they need," she said.

"I will never forget the first time I read Macy's file from the ACC (Animal Care and Control) and how a second evaluator decided to take her off the PTS (put to sleep) list. I don't know who that evaluator is, but every time I think about that person, I am grateful."

Take a look at the photo that drew the U.N.'s attention, and you see the full set of stamps below.

Macy pit bull International Day of Happiness

Photo: Jaymi Heimbuch

International Day of Happiness stamps

International Day of Happiness stamps

Related on MNN:

Laura Moss writes about a variety of topics with a focus on animals, science, language and culture. But she mostly writes about cats.

This is the face of world happiness -- and she would like to sit in your lap
The U.N. chose a photo of a rescued pit bull to grace 1 of 6 stamps to mark International Day of Happiness stamps.