Normally quiet, the bond market can occasionally send warning signals loud enough to hit stock markets worldwide and even grab the attention of U.S. presidents and other world leaders

U.S. Treasury bond sell-off coincided with the nonpartisan Congressional Budget Office's release of statistics that the national debt is about to cross $40 trillion.

Normally quiet, the bond market can occasionally send warning signals loud enough to hit stock markets worldwide and even grab the attention of U.S. presidents and other world…