McDonald’s Corp. (MCD) is celebrating its 50th anniversary by rolling out its own "global currency," dubbed MacCoin, which will be available while supplies last.

According to the Chicago-based fast-food chain operator, starting Aug. 2 customers can receive a MacCoin with the purchase of a Big Mac at 14,000 restaurants around the U.S. while supplies last. Customers can redeem the MacCoin for a free Big Mac at participating restaurants in the U.S. and in more than 50 countries. (See also: McDonald's Stock May Fall 9% After Earnings.)

McDonald’s Coins a Nod to the Past

McDonald’s is rolling out five commemorative coins that have designs each representing a decade of Big Mac by pulling in history, art, music and pop culture from the different time periods. For example for the '70s MacCoin, it features flower power while the '80s coin focuses on pop art and the '90s coin is defined with abstract shapes and bold colors. The coin for the 2000s celebrates technology that defined that decade while the 2010s MaCoin is a nod to the evolution of communication, said McDonald’s in the press release.

“Since it was introduced at a family-owned McDonald’s restaurant 50 years ago, the Big Mac has traversed the globe and is enjoyed in cities from Shanghai to Chicago, providing delicious, feel good moments to people all over the world,” said McDonald’s President and CEO Steve Easterbrook in a press release. “So we wanted a global celebration as unique as the burger itself. The MacCoin transcends currencies to commemorate our global iconic burger while giving customers all over the world a chance to enjoy a Big Mac on us.”

Long a Way to Gauge Global Purchasing Power

In an interview with USA Today, Easterbrook said the MacCoin idea was born out of the fact that the Big Mac has played a global role in measuring purchasing power of consumers for years. The executive pointed to the Big Mac Index that The Economist began using back in 1986 to gauge the purchasing power of international currency. "They use it to this day," Easterbrook said in the interview. "Why not have some fun with it? Create our own currency." According to McDonald’s, it sold 1.3 billion Big Macs in 2017. (See also: McDonald's Salads Linked to Intestinal Illness Outbreaks in Two States.)

Last week McDonald’s reported second-quarter earnings that beat Wall Street expectations by 7 cents, reporting EPS of $1.99 on revenue of $5.35 billion. Revenue declined 11.5% year-over-year and was blamed on franchising agreements. Global same-store sales rose 4% during the June quarter.