But BofA isn’t alone. Citigroup kind of got lost in the BofA hubbub today, but it fell nearly as much, down a whopping 16 percent. These are banks with $2 trillion in assets, folks. One-day market moves of 16 percent and 20 percent are enormous for companies of this size, and they’d already been falling sharply in in recent days. Bank of America has lost nearly one-third of its market capitalization in the last three trading sessions, while Citigroup is down a quarter. JPMorgan Chase, also in the $2 trillion TBTF club, fell 9 percent today and is down 15 percent over three sessions.

What’s on their books? That’s the question we’ve wanted to know about our paper-it-over, extend-and-pretend economy for years now. And yet we still don’t know.

Here’s Bloomberg’s Jonathan Weil two weeks ago (note that BofA shares are now at $6.51 a share):

At $9.85 a share, down 26 percent this year, Bank of America finished yesterday with a market capitalization of $99.8 billion. That’s an astonishingly low 49 percent of the company’s $205.6 billion book value, or common shareholder equity, as of June 30. As far as the market is concerned, more than half of the company’s book value is bogus, due to overstated assets, understated liabilities, or some combination of the two.

Now that 49 percent number, “astonishingly low” just two weeks ago, is at 32 percent of book value.

Meantime, five years into its downturn the housing market—the root of this crisis—is still in a shambles with no end in sight.

Watch the bank stocks in the coming days and weeks. They’re signaling that things are not well with the financial system.

Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu.