Other markets have also been signaling worry.
It also may signal worry at home, experts said, citing concerns intensified by a stock-market collapse and economic slowdown.
The question should be, in cases when the markets aren't signalling worry but the agencies downgrade anyway, how often are they right?
In what seems a worrisome trend, many bonds of private equity-backed companies have recently plummeted in value, signaling worries about their solvency.
They are signalling worries about, for instance, overlapping board members at Apple and Google, or the indefinite retention of search histories by search engines.
China's official Xinhua news agency issued comments from Deputy Foreign Minister Zhang Yesui that did not expressly single out North Korea but nonetheless signaled deepening worry about its actions and the response from the United States and its allies.
Yet her allies fear that to appear to campaign openly would appear presumptuous and provoke Mr. Paterson, who had already signaled his worry, before Ms. Kennedy made her interest clear on Monday, that the jockeying over who would succeed Mrs. Clinton had become undignified.
Zucker signaled deep worry inside the network over the matter, initially saying he needs to speak carefully in public about just "how serious a concern we think this is".
Investors have also signaled their worries about the American economy through the dollar's cascading fall against the euro, yen and British pound.
U.S. stocks moved sharply lower after the Fed statement signaled renewed worries about the economic outlook while leaving the option of a second rate increase in March on the table.
U.S. Secretary of Education Arne Duncan on Tuesday expressed concern at record student debt levels, signaling growing worry within the Obama administration and perhaps adding momentum to efforts meant to alleviate debt burdens.
