McDonald's MacCoin: 50th anniversary of Big Mac marked with limited edition currency

A limited edition coin will buy you a free Big Mac - if you can get your hands on one

To mark the 50th anniversary of the iconic Big Mac, McDonald's are giving US customers something exciting with their meals today.

At 14,000 participating restaurants across the US, customers will receive a MacCoin with the purchase of a Big Mac. This special edition coin can then be used to get a free Big Mac any time between Friday and the end of 2018.

The brass coloured coins will feature five unique designs, each one reflecting one of the decades since the Big Mac has been sold

According to USA Today, the '70s coin will showcase flower power, the '80s coin will allude to pop art, the '90s coin will be defined by bold, abstract shapes, the early '00s coin will focus on technology, and the '10s coin will depict the evolution of communication.

What is the Big Mac?

The Big Mac is made up of two beef patties, special sauce, iceberg lettuce, American cheese, pickles and onions, served in a three-part sesame seed bun.

Since it was first sold in 1968, it has become the jewel in the crown of the McDonald's menu, and has come to be seen as an icon of Americana around the world.

It has also been used as a reference point for comparing the cost of living in different countries. The so-called Big Mac Index was introduced by The Economist in 1986 as an informal way of comparing two currencies.

The Big Mac is usually served as part of a meal with fries and a soft drink (AFP/Getty Images)

Is the Big Mac different around the world?

The Big Mac is a geographically localized product, but it generally follows the same recipe around the world. The only notable difference is the cost.

The most expensive Big Mac in the world is in Switzerland, costing around the equivalent of $6.80 in US dollars.

The cheapest Big Mac in the world is in Ukraine, where it comes in at around $1.60.