McDonald's has created an outrageous diamond and sapphire-studded Big Mac ring worth US$12,500 in a Valentine's Day stunt that encourages true Big Mac lovers to pledge their commitment by putting a ring on it.

Seven layers of the fast food giant's iconic sandwich have been bedazzled as white diamonds, orange and green sapphires and encrusted in an 18K gold "Bling Mac" that can be won by sending funny and creative vows of love and commitment on Twitter.

The single-most creative and hilarious tweet will be deemed the winner.

The publicity stunt is to promote the three sizes of Big Macs (Mac Jr., Big Mac and Grand Big Mac) ahead of Valentine's Day.

It's not the first time McDonald's has gone into the jewelry business.

Last year, Welsh fashion designer Julien Macdonald redesigned the chain's packaging with baroque-style, black and white sandwich boxes studded with rhinestones as part of the UK's launch of 'luxury' premium burgers.

To enter this year's contest, fans are invited to tweet to @McDonalds using the hashtag #BlingMacContest.