Some economic indicators may give you a clear and useful picture of where the market -- and your investments -- might be headed. Others, alas, just involve bikini models.

The Bespoke Investment Group says it's discovered a "Sports Illustrated Swimsuit" indicator. Between 1978 and 2009, when the magazine's annual swimsuit issue has sported an American on the cover, Bespoke says the S&P 500 has averaged a 10.6% return for the year. When the cover model's a non-American, the return drops to 8.2%.

While a combination of attractive models and potential wealth may be near-irresistible to many investors, closer scrutiny reveals that this prospective indicator is flimsier than most of those cover models' attire. It's more than possible that any connections Bespoke thinks it has found result solely from coincidence.

If you really need to get your investing clues from magazines, consider instead their thickness. An improving economy may spur more companies to take out a greater number of ads in major periodicals, which can bump up those magazines' page counts. I noticed that the March Vanity Fair issue seemed significantly thicker than the February one. But at less than 200 pages, the April issue looks unusually svelte, despite ads from retailers such as Gap (NYSE: GPS), Estee Lauder (NYSE: EL), and Target (NYSE: TGT).

Trading clues
You'll find an even more logical indicator by monitoring business at brokerages such as TD AMERITRADE (Nasdaq: AMTD), E*TRADE Financial (Nasdaq: ETFC), and Charles Schwab (Nasdaq: SCHW). As my colleague Rick Munarriz noted, these brokers' business was strong in January, reflecting a boost in trading activity and (perhaps) increased bullishness among investors. February's numbers dropped for Schwab, though, suggesting that investors are still skittish. Make sure you give these numbers more than a cursory glance; brokerages' current price war over commissions means that lower fees could initially mask gains in trading value.

Finally, from the "pride goeth before the fall" department, one theory suggests that plans to build the world's tallest skyscraper in any given location will precede an economic downturn in that region. While that may sound illogical, such grandiose plans could reflect a market that has risen too far for too long, lulling investors into false expectations of eternal prosperity.

Economic indicators are often more amusing than informative, and they're not always the best way to glean clues about your investments. Focusing instead on the actual businesses at hand, and weighing their performance and promise against that of their peers, might serve you far better.

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article. Charles Schwab is a Motley Fool Stock Advisor pick. Try any of our investing newsletter services free for 30 days. The Motley Fool is Fools writing for Fools.