Harley-Davidson (NYSE: HOG) is an iconic American brand. Yet challenges surrounding the company and its beloved baby boomer demographic could make investing in this stock an accident waiting to happen.

The Harley-Davidson brand is as American as Coca-Cola (NYSE: KO) or McDonald's (NYSE: MCD), with rabid, loyal fans much like those who follow the stocks (and adore the products) of companies like Apple and Sirius XM. As an investor, if you can recognize when customers "bleed the brand," then it's a sign there's something special going on, which could lead to winning investments. Harley-Davidson evokes the same reaction: dedicated, tattooed fans revving their hogs and professing their love for all things Harley.

But inked skin eventually sags, and Harley's core demographic is aging.

A recent Fortune article rode through the history of Harley-Davidson, listing the brand's ups and downs (including its 1990s turnaround). Harley-Davidson's core customers are middle-aged men, and it gets a heck of a lot harder to be an easy rider with every passing year. While Harley resonates for the massive baby boomer generation, younger customers apparently just don't feel the same fervor for the brand.

Those are salient points for investors to consider, and with Harley's declining earnings, it's facing a double whammy, given aging customers and the lackluster overall economy.

Harley-Davidson's not even a cheap stock idea right now. Its revenues and earnings have been falling steadily for several years running. In the last 12 months, sales fell 15.7% and earnings per share dropped 73.1%, to a measly $0.50 per share. At its recent high-water mark, in 2006, it reported earnings of $3.93 per share, and profitability has been on a downward spiral.

Although analysts expect Harley-Davidson to report $1.24 per share in earnings this year, sales are still expected to decrease. Meanwhile, Harley-Davidson's PEG ratio is currently 2.29, which doesn't suggest a bargain stock.

The nasty economy has also put boomers in a precarious financial position as they transition into retirement. I recently discussed this demographic danger, and suggested wariness for stocks like Talbots (NYSE: TLB). Some companies simply cater too strongly to this weakened consumer group that may have increasing difficulty justifying discretionary purchases. With its expensive bikes, Harley-Davidson fits that description perfectly.

Granted, Harley has turned its business around before. Maybe it can do it again, perhaps by appealing more strongly to younger thrill-seekers. Then again, perhaps it faces hurdles that even Evel Knievel couldn't clear, such as reinvigorating the brand for younger people. What do you think? Sound off in the comments box below.  

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Alyce Lomax does not own shares of any of the companies mentioned. The Fool has a disclosure policy. True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community.