By Heidi N. Moore, contributor

We’ve all seen those commercials where shouting announcers urge consumers to trade in their old gold for cash. Who knew that central banks would be the ones who took them up on it?

Well, sort of. The Bank of International Settlements has bought 349 metric tons of gold from governments, which raised $14 billion. The gold sales, usually rare, are occurring at a record rate. (Someone should tell Russia, which is still on a buying spree.) The banks plan to buy the gold back later in swap agreements, but if they don’t, the BIS could well sell the gold, which could then flood the market.

What’s interesting about this is that it flies in the face of conventional market wisdom that holds that the gold rush was a “flight to safety,” that governments considered gold more trustworthy than currency.

Deutsche Bank Securities analyst Jorge Beristain, who covers metals and mining companies, is bullish on gold and the companies who mine it. He wrote this week: “We believe European sovereign risk and inflows into gold ETFs have been the main drivers of stronger gold prices in 2Q10. We expect U.S. dollar weakness will be the catalysts for even higher gold prices going forward.”

Yet we have central banks offloading their gold, right in the middle of a sovereign crisis, to pay off their bills. When it comes right down to it, is gold paling beside the necessity of cold, hard cash?

Beristain says no: “Within our coverage, gold is our most favored metal and though gold prices have rallied to a new all-time nominal high, we do not believe gold prices can be considered excessive. Amid near-term macro headwinds (sovereign-debt crisis in Europe, credit tightening in China, and a cluster of soft economic indicators in the U.S.) flight to safety should propel gold prices to higher levels through 2012, in our view.”

The market, so far, has agreed. The SPDR Gold Trust ETF (GLD) is up 9% this year (see chart above), and gold is selling at $1,194 an ounce. Beristain predicts prices will rise to $1,450 in 2011 and $1,600 in 2012. He also currently favors Newmont Mining (NEM) and Barrick Gold (ABX) as his top stock picks to take advantage of gold’s popularity. Ironically, however, even some gold and other metals miners are, like those central governments, hoarding cash.

If central banks are trading their gold in, it might be bad news for the price of gold, but looking deeper, it may be good news for the world economy. For one thing, it means that central banks are actually trying to pay their bills. For another, gold is well-known as a fallback in times of extreme crisis — and if central banks are selling gold, perhaps they are not as concerned as they once were about the prospects for another market-freezing disaster. Of course they could also be leaving themselves wide open.

So gold may still continue its upward run next year and after, and in the near term, investors should really be worried about the root causes of the movements in gold prices: what all those central banks are thinking.

–Heidi Moore is Sweeping the Street while Colin Barr is on vacation.