Once the card-holder has six stamps, they get a free beverage from any of the shops, reports Alex Baldinger at The Washington Post.
"The card is a fun way to get baristas and customers talking with each other," a participating barista told the paper.
The card is seen as a backlash to Starbucks' popular loyalty card, writes Arin Greenwood at The Huffington Post.
The coffee mega-chains loyalty program includes perks like free refills, free food, and more.