I found it! It was just a matter of using the right search terms:
$2.5 trillion in Social Security bonds stored in filing cabinet in downtown Parkersburg, W.Va.
Remember Al Gore's "lockbox," the one he was going to use to protect Social Security? The former vice president talked about it so much during the 2000 presidential campaign that he was parodied on "Saturday Night Live." Gore lost the election and never got his lockbox. But to illustrate the government's commitment to repaying Social Security, the Treasury Department has been issuing special bonds that earn interest for the retirement program. The bonds are unique because they are actually printed on paper, while other government bonds exist only in electronic form.
They are stored in a three-ring binder, locked in the bottom drawer of a white metal filing cabinet in the Parkersburg offices of Bureau of Public Debt. The agency, which is part of the Treasury Department, opened offices in Parkersburg in the 1950s as part of a plan to locate important government functions away from Washington, D.C., in case of an attack during the Cold War.
One bond is worth a little more than $15.1 billion and another is valued at just under $10.7 billion. In all, the agency has about $2.5 trillion in bonds, all backed by the full faith and credit of the U.S. government. But don't bother trying to steal them; they're nonnegotiable, which means they are worthless on the open market.
[...]
The national debt - the amount of money the government owes its creditors - is about $12.5 trillion, or nearly $42,000 for every man, woman and child in the country. About $8 trillion has been borrowed in public debt markets, much of it from foreign creditors. The rest came from various government trust funds, including retirement funds for civil servants and the military. About $2.5 trillion is owed to Social Security.
Good luck to the politician who reneges on that debt, said Barbara Kennelly, a former Democratic congresswoman from Connecticut who is now president of the National Committee to Preserve Social Security and Medicare. "Those bonds are protected by the full faith and credit of the United States of America," Kennelly said. "They're as solid as what we owe China and Japan."
Interesting read. It does not change the following:
1) Social Security is just another federal government expenditure - although one of it’s largest.
2) Current federal expenditures are a whopping 145% of revenue (45% deficit)
Even if there are a stack of T-Bills in a drawer it does not change those two points!