One thing that has caught my attention of late is the rapid jump in US interest rates.

Bond prices have tumbled, and yields have risen, in the last two weeks, at the fastest pace since June of 2013, back when the bond market had its so-called "taper tantrum."

That's when then-Fed Chairman, Ben Bernanke, indicated that the Fed's Quantitative Easing, or bond-buying, program would soon be wound down.

Amid increasingly louder drumbeats predicting a mid-year move by the Fed to start raising short-term rates, bond yields have gone from under 1.8% a scant two weeks ago, to about 2.15% at today's settlement.

This is a disturbing sign given that economic data, of late, have not been universally strong; overseas economies, while steadying, are far from growing at an acceptable pace; and geo-political risk suggests that investors park some funds in Treasuries for safe-keeping.

It is possible that all those concerns will soon be alleviated by aggressive monetary easings in Europe, China, Japan, Russia and Britain and Australia ... taking the onus off the Fed to remain Atlas among the world's central bankers.

Also, some cash-strapped foreign investors may be dumping US assets to shore up their cash balances, which are dwindling at home ... particularly in places like Russia.

At the moment, it is hard to tell if rates are getting ready to spike beyond current levels. But it bears close scrutiny.

US stocks are roughly fairly valued if, and only if, domestic interest rates and inflation rates remain quiescent.

If the yield on the 10-year note were to top 2.25%, one might wonder whether some defensive steps in the stock market might be appropriate in the short run.

We're not there yet ... but if we arrive at that point sooner, rather than later, it will be time to start hedging some bets and protecting those hard-won profits.