All right, I'm going to go ahead and call it -- when any one industry starts to snatch up all the naming rights for sports stadiums, it's time to start selling stocks in that industry.

At the height of the dot-com bubble, tech names started showing up all over sports stadiums, but that party ended and ended badly. Though it has been a bit more gradual, there has been a bubble forming in the financial industry for the past decade (you don't say!). At the same time, we've seen a steady increase in financial companies ponying up to get their names on sporting complexes.

What exactly am I talking about? Check this out:

PNC (NYSE:PNC), Raymond James, and Comerica all became namesakes in the late '90s. Invesco took center stage at the Denver Broncos' stadium in 2001. Edward Jones and Lincoln Financial snagged their pieces of the pie in 2002. Citizens Bank bought naming rights for the Philadelphia Phillies stadium in 2003. M&T Bank also grabbed space in 2003 -- conveniently enough after bankrupt Internet service provider PSINet left the Baltimore Ravens high and dry. Bank of America (NYSE:BAC) took over the Carolina Panthers stadium from Ericsson in 2004. In 2005, Quicken Loans bought the naming rights for the Cleveland Cavaliers' arena.

And of course, we can't forget the 2006 $400 million deal for Citigroup (NYSE:C) to get its name on the New York Mets'  new stadium.

At this point, I'm sure just about everyone knows what Bank of America and Citigroup's stocks look like since their naming deals. But they're not alone. M&T is worth less than half of what it was at the beginning of 2003. Lincoln has shed two-thirds of its value since its 2002 naming deal, and Invesco is off 70% since 2001. Even PNC and Comerica, which have the luxury of a whole decade since they bought naming rights, are off roughly 40% and 70%, respectively, since then.

The point isn't that no company should ever purchase naming rights to a sports stadium -- companies like Heinz, Gillette, and Pepsi all have namesake stadiums and haven't fallen apart. And even though Ford (NYSE:F) has fallen apart, I wouldn't link that to it being the face of the Detroit Lions stadium (though the performances of Ford and the Lions are eerily similar).

However, when there's so much extra income sloshing around in a single industry that it starts to dominate sports arenas, it could be a good sign that the industry in question is getting a little ahead of itself. Of course, at this point, we don't need my stadium-naming theory to surmise that bank stocks aren't the best way to go; even just a quick glance at stock ratings in The Motley Fool's CAPS community could tell you that. Citigroup carries a lowly two-star rating (out of five), as does M&T, PNC, and Comerica. Bank of America may be one of the better-liked bank stocks, but even that has only nabbed it three stars.

My bet is that with the financial industry trying desperately to keep its head above water, we'll see far fewer banks jumping at naming rights in the coming years, and maybe we'll even see a new industry take over. So, if we start to see Novartis (NYSE:NVS) Field, Genentech (NYSE:DNA) Arena, and Stryker (NYSE:SYK) Park all sprout up in short order, I'd want to keep a close eye on the health-care industry.

Further financial Foolishness:

PepsiCo, Invesco, and H.J. Heinz are Motley Fool Income Investor recommendations. Bank of America is a former Income Investor recommendation. The Fool owns shares of Stryker. Try any of our Foolish newsletters today, free for 30 days.

Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. The Fool’s disclosure policy has never once been caught with its pants down. Of course, it doesn't actually wear pants …