There is an old saying that stock buybacks are a good sign because they are proof a company’s best investment is in its own shares. Put another way, management thinks the market is undervaluing its stock – so it is more than happy to buy at bargain prices while they last.

The trouble is, most – if not all – CEOs and directors have little incentive to say the company is anything other than oversold. Find a corporate executive admitting he made a mistake and the best-case scenario is that he’s at a podium announcing his retirement.

More than likely, he’s sipping a daiquiri in St. Croix.

Yes, some stock buybacks are smart decisions made by good companies with good leadership. But some are just moves to boost EPS figures for the quarter – since, after all, if you can’t grow the E in “earnings per share,” you can always subtract the S via buybacks that take shares off the market. Other buybacks are merely meat for the PR grinder, where a company announces a plan to buy back billions of dollars of stock and then puts very little actual money toward the repurchase after the SEC filing.

Here are five big-name companies whose buybacks may never deliver any value to shareholders: AOL (NYSE:AOL), TiVo (NASDAQ:TIVO), Southwest Airlines (NYSE:LUV), Covidien (NYSE:COV), and Hewlett-Packard (NYSE:HPQ).

AOL

AOL announced on Aug. 11, after its share price hit the lowest value since the company was spun off from Time Warner in 2009, that it would begin a $250 million stock buyback program. The company has about 107 million shares on the market, so the program could potentially snap up about 19% of the outstanding AOL stock at current valuations.

I could be cruel and suggest that if CEO Tim Armstrong and his team wait a few weeks, until AOL hits, say, $10 a share, that $250 million will buy an even bigger percentage – and that if they wait a few more months for AOL to hit $9, it will go even farther than that. But let’s stay on topic here…

This buyback comes just a few months after the $315 million buyout of the Huffington Post and alongside a Wall Street Journal report that indicates the company is burning $160 million a year on Patch.com, it’s community news network.

Perhaps AOL is convinced that its investments will pay off, and that the $250 million buyback plan is a great strategic move as it retools for future growth. With $800 million in cash on its balance sheet, Armstrong could certainly execute this move in full without bleeding the coffers completely dry.

Of course, one has to be skeptical. As its legacy dialup internet access biz slowly fades into the ether and no new revenue streams have emerged, AOL could just be hoping to juice its EPS figure with a buyback.

AOL has been stuck in a steady downward spiral for years, and it seems hard to justify spending $250 million on window dressing for the balance sheet when clearly there are so many other issues in play.

TiVo

TiVo was once one of those iconic brands, like Xerox or Kleenex or Band-Aid, that managed to connect so strongly with consumers that its name became the product. But TiVo has been struggling to find profitability recently and could be left behind amid the streaming video revolution.

The good news is that TiVo has zero debt and $200 million in cash on its balance sheet, so it has some time left on the clock to mount a comeback. Of course, the TiVo board just announced a filing that could burn up to half of that cash in a $100 million stock repurchase program over the next two years.

If the plan was meant to impress shareholders, it worked. From Thursday, Aug. 11, to Monday, Aug. 15, shares rallied about 16% due in part to the news.

But come on. TiVo will never dive into a buyback of that size. The company has 120 million shares outstanding, and at current valuations that would account for 10% of outstanding TiVo stock. What’s more, it would wipe out half of its piggybank at a time when the company has posted losses in 10 out of the last 11 quarters and is targeting another losing year in fiscal 2012.

TiVo had posted wider losses in recent quarters, lower revenue, higher costs and fewer subscribers. Yes, TiVo swung to a first-quarter profit for the first time in ages – but that was due to a recent legal settlement with Dish Network (NASDAQ:DISH) – and $500 million legal windfalls aren’t going to come around every quarter.

Yes, a buyback may improve EPS figures. Yes, there may be more cash to burn after the DISH settlement. But if shareholders think a stock repurchase is going to change those other ugly numbers, they should think again.

Southwest Airlines

Southwest announced on Aug. 5 that it would buy back up to $500 million of its own shares. The company has about 804 million shares – and at current valuations, executing the full buyback would snap up over 7% of outstanding LUV stock.

It’s worth noting, of course, that the Southwest Airlines board authorized a similar $500 million program in early 2008 that spent only about $54 million of the pot as an economic downturn and soaring oil prices made the carrier’s outlook rather grim.

Could the buyback be a big vote of confidence by management? Maybe. Southwest is head-and-shoulders above other major carriers, both in customer satisfaction and in its balance sheet over the past few years. There are big reasons to expect Southwest to lead the charge when the airline industry inevitably returns.

Of course, Southwest could always halt the buyback after first blush, as it did in 2008. And if you believe in inflation and are pessimistic about consumer spending – two common feelings for many investors these days – then there’s a good chance Southwest could follow the same path it did three years ago and abort its buyout before it has a substantive impact.

Covidien

It’s hard to not laugh out loud when you read the line from the CEO of pharmaceutical and medical device giant Covidien regarding its $2 billion stock buyback plan. Top exec José E. Almeida said Covidien has “no intention of accumulating cash.” At the end of June it was sitting on almost $1.8 billion in cash and equivalents – while it’s dividend has been steady for well over a year at a rather lackluster yield of 1.5%!

The company has over 493 million shares outstanding, so the $2 billion plan would account for about 8% of Covidien shares if fully executed and if the stock remains around current valuations.

Covidien is trying to make its way in a highly competitive healthcare industry, subject to pricing pressures and the ever-looming impact of patent expirations. One way to lift the long-term outlook of this stock would be to invest in research to generate the next big biotech breakthrough. Another is, of course, to buy back outstanding stock to improve earnings per share.

Yes, research could fail to pan out and rejiggering the balance sheet is a sure way to “improve” your EPS. But which do you think would have a more lasting impact on shares?

To be fair, Covidien spent nearly $450 million on research and development in 2010, or about 4.3% of total revenues. But as any healthcare stock owner should know, it’s a never-ending fight to stay at the top of the Big Pharma food chain.

COV stock has outperformed the market this year, but investors should hope that the company is not more concerned with keeping up appearances than keeping up its drug pipeline or returning profits to shareholders via bigger dividends.

Hewlett-Packard

Poor Hewlett-Packard. The stock is off 25% in the last year. The company has made big buyout moves lately, from a $1.2 billion deal to buy Palm to a $2.35 billion push for 3PAR and a $2.7 billion deal to buy 3Com, but none have really moved the needle yet.

But don’t cry for HP. As of April it had over $12 billion in cash on its balance sheet, enough to scrape together a $10 billion offer for software maker Autonomy. That’s in addition to authorizing up to $10 billion in stock buybacks the week before.

Wait, how does that math work? Oh wait … it doesn’t.

With just over 2 billion shares on the market that would account for almost 16% of outstanding HPQ stock at current valuations. But there clearly isn’t enough in the change purse to fund this bet.

It’s worth noting that though this $10 billion filing may never come close to its full potential, it is in addition to the $10 billion authorized last August for the same purpose, of which the company had more than $4 billion remaining at the time of the next buyback announcement.

Still, there’s little chance of the recent repurchase plan announced at the end of July being paid in full after this deal.

Of bigger concern to investors shouldn’t be the lack of a big buyback but the fact that HP is flinging around tens of billions of dollars so freely. After spending more than $6 billion on big-time acquisitions of Palm, 3PAR and 3Com, there is now this planned deal with Autonomy and rumors of a PC spinoff. That sounds like an organizational nightmare for the stock if ever there was one, and we won’t know how the “new” HP will look for quite some time.

Jeff Reeves is the editor of InvestorPlace.com. Follow him on Twitter via @JeffReevesIP and become a fan of InvestorPlace on Facebook.