Nervous investors piled into bond ETFs in 2011. Yet if Treasury yields rise and bond prices fall, it would likely signal investors are growing more optimistic on the global economy and a resolution of Europe’s debt crisis. This increased appetite for risk would be good news for stock-based ETFs. Many investors are hiding out in low-yielding Treasuries and cash.

From a technical perspective, iShares Barclays 20+ Year Treasury is “skating on thin ice,” writes ETF Digest’s Scott Pluschau at The Street.

He points to a developing “head and shoulders” pattern in the bond ETF that could break key support levels.

There are several ETFs that short Treasuries – they rise when bond prices fall. The largest by assets include ProShares UltraShort 20+ Year Treasury (TBT), ProShares UltraShort 7-10 Year Treasury (PST), ProShares Short 20+ Year Treasury (TBF) and Direxion Daily 30-Year Treasury Bear 3X (TMV).

iShares Barclays 20+ Year Treasury