CNN  —  The decidedly unsexy bond market is usually pretty quiet. But when they want to, bond investors can send a loud, clear message to Washington. They did just that Thursday. The 20-year bond auction conducted by the US Treasury on Wednesday afternoon was unusually weak: Demand for the bonds was the lowest since February, according to the Treasury Department. Investors who bought the bonds sought a higher-than-expected yield – effectively saying they wanted to be paid more for taking on the