Announced in a regulatory filing Wednesday, The Winklevoss Index Winkdex will serve as the basis for an exchange-traded fund the twin brothers are planning for later this year.
The Winkdex will represent a "blended price" for Bitcoins based on the prices on the top three US exchanges for the currency, by volume.
Late Wednesday the price was $624.49, up 0.84 percent from late Tuesday.
The Winklevosses are tech sector venture capitalists initially famous for their claim to having had the original idea for Facebook, and have picked up tens of millions of dollars from Facebook to settle that claim.
(Also see: Winklevoss twins take Facebook back to court)
Since then they have invested large sums in Bitcoin-related ventures as well as the currency itself.
(Also see: Winklevoss twins say Bitcoin could become a country's currency)
Last year their Math-Based Asset Services filed a plan with the Securities and Exchange Commission to market the $20 million Winklevoss Bitcoin Trust, which will hold the currency as an investment.
Amid regulator wariness over Bitcoins, the trust has yet to gain formal approval.
The first operational ATM in the United States started up Tuesday in a New Mexico cigar shop, according to manufacturer Lamassu Bitcoin Ventures.
Lamassu has some 200 orders around the world, and has opened Bitcoin ATMs in two Australian cities as well as one each in Helsinki, Berlin, Bratislava and Vancouver.
The New Mexico operator Enchanted Bitcoins is "paving the way for mainstream Bitcoin accessibility in the Unites States," says Zach Harvey, CEO of Lamassu, a company registered in the British Virgin Islands.
The operator is following guidelines from FinCEN, the Financial Crimes Enforcement Network, to avoid running afoul of the law, and has registered as a money exchange service.
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