Many investors know about the key metrics that provide clues about the U.S. economy's health, and where it's likely to head in the near term. Retail sales, housing starts, UPS (NYSE: UPS) and Fed Ex (NYSE: FDX) deliveries and, of course, those infamous corrugated box orders, all provide clues about demand at the retail and wholesale levels, and are positively correlated with increases in U.S. GDP.

What's another metric worth monitoring? Office rents -- and here, like the recent statistics reported for the above metrics, the numbers are not good.

Office rent charges per square foot in Midtown Manhattan, London's West End, and Central Tokyo fell in Q3 for the first time since 2002, a report from CB Richard Ellis indicated Tuesday (pdf).

In New York, Midtown Manhattan office rents fell 2.7% to $98.08 per square foot. Midtown Manhattan includes the headquarters of many of the world's multinational corporations and the Broadway theater district, but does not include the Wall Street financial district, which is located in Lower Manhattan.

In London's West End, occupancy costs declined 5.1% to $248.66 per square foot. In Central Tokyo, costs dropped 5.3% to $184.26 per square foot.

Economist Richard Felson told BloggingStocks Tuesday the fact that rents are declining the world's top three financial centers for the time since 2002 is not a good sign. "It's further evidence of the spread of the recession," Felson said. "Very rarely do you see rates in all three cities declining at the same time. Then again, very rarely do you see all three regional economies in recession at the same time, either, which shows you the fix we're in."

Welcome to Way Off Wall Street, a column dedicated to providing Main Street opinions on topics of interest to investors. Each installment highlights the views of Americans who are far removed from the canyons of Wall Street -- and who often see things more clearly as a result.

The current economic downturn began in real estate, ripping through the construction industry as it went. The banks began to crumble next, as declining real estate values pulled their phantom capital support structure from beneath them.

Then Wall Street began quaking, as good faith and trust were swept aside by the realities of mismanagement, fraud, and corruption. Then the insurance industry began to take a kick in the teeth due to its ties to Wall Street's derivatives securities mill. Soon, we'll all bear the brunt of yet another round of insurance premium increases as a result.

Office vacancy rates rose [subscription required] nationally for the first time in four years in Q4 2007, The Wall Street Journal reported Monday.

Citing data provided by Reis Inc., a New York real estate research firm, The Journal reported that the addition of an unusually large amount of new space and tenants shying away from lease signings pushed the national vacancy rate to 12.6% in Q4 2007 from 12.5% in Q3 2007.

The survey indicated that the increase came after 16 consecutive quarterly vacancy rate declines and also noted that the subprime mortgage-affected West (Los Angeles) and South (Fort Lauderdale, Fla.) saw vacancy increases of 1.9 and 1.7 percentage points, respectively.

Economic Analysis: The pertinent information here is not the size of the vacancy increase, but the fact that the office vacancy rate rose. While qualifying the above by noting that it's only one quarter -- and one quarter does not a trend make -- the vacancy rate increase, when viewed against a backdrop of other sluggish / sub-par data on residential housing, corporate profits, job creation, retail sales and consumer confidence, paints a decidedly modest economic picture. It's another data point that suggests that the U.S. economy is already in slow-growth mode, or perhaps worse.