What investors hold in their hands when they entrust the fate of their retirement to the Malvern mutual fund giant Vanguard Group is not just an ultra-efficient financial instrument but a jewel of untold worth.

That’s because with Vanguard’s unparalleled business model, its true value is left entirely to your imagination.

As a private company, “the shares in Vanguard held by the funds cannot be sold or transferred to third parties, so there is no ‘market’ value for the shares and, as a result, no public valuation of the firm by any standard measure,” spokesman John Woerth said in a Philly.com special feature.

And in light of Vanguard’s new record accumulation of total assets — $3.4 trillion — imaginations are beginning to run wild.

To satisfy the growing curiosity, reporter Joseph DiStefano pieced together hints to help put a finger on what Vanguard might just be worth. Contrasted against the $3.5 billion value of the smaller Federated Investors and the $58 billion of publicly-traded market leader BlackRock, Vanguard could be valued at tens of billions of dollars.

Recognizing that Vanguard technically doesn’t assess its own value, those tens of billions are a far cry from the equivalent number reported to the Securities and Exchange Commission: a paltry $250 million that Woerth calls “the total amount of capital contributed to Vanguard by all of the member funds.”

Where in between Vanguard’s value truly rests is anyone’s guess. But one thing’s for certain: “Vanguard investors hold in their fund portfolios shares of a vastly successful corporation — their own — whose equity appreciation they are not to touch. Or count,” DiStefano wrote.

Delve much deeper into how Vanguard values other private companies and what it might be worth itself on Philly.com here, and check out previous VISTA Today coverage of Vanguard’s growing acclaim here.