Two key issues have been in play in the stock market as we head into the long Labor Day weekend. Insider buying has been robust in the past month, yet the market has moved steadily downward. The S&P 500 has slid 5% since Aug. 2.

As a result, many recent insider purchases are now “underwater.” That spells opportunity. If these stocks are even cheaper than the levels in which insiders found them to be appealing, then we may witness even deeper insider buying in coming weeks, further validating this “buy” signal. Here’s a look at six examples.

1. Aircastle (NYSE: AYR )

In early June, this aircraft leasing firm agreed to sell a 15% stake in itself to Japan’s Marubeni Corp. The two firms aim to leverage each other’s global transport divisions, cross-selling services and equipment to each other’s customer base. Marubeni began buying shares in subsequent weeks, and by early August, already qualified as an insider as its ownership stake moved above 5%. Throughout the past month, Marubeni has kept on buying, even as shares moved past the $17 mark. Yet in recent days, the market turmoil has pushed shares down close to $16. Look for Marubeni to keep buying until it hits the 15% ownership threshold. Meanwhile, analysts have yet to project the benefits of these two firms’ partnership, as forward earnings estimates have remained largely static over the past 90 days.

2. Halcon Resources (NYSE: HK )

Insiders bought more than $2 million of this energy exploration firm in early August as part of a secondary share offering priced at $5.10 a share. In the past 10 days, as shares have slipped below the $5 mark, insiders have continued to accumulate shares. Halcon has a legion of fans in the financial blogosphere, and this recent post typifies the bullish sentiment of some. The company’s strong positioning in the highly productive Utica Shale region is what has them enthused, though Halcon’s oil and gas production in recent quarters has been a bit disappointing. This is now a “show me” stock after that secondary share offering pushed shares down to lows form which they have yet to recover.

3. CST Brands (NYSE: CST )

The gas station operator was spun away from parent Valero Energy (NYSE: VLO) in May, and though shares eventually moved up above $33, they’ve been backsliding recently. A company director thought he spotted value by the time shares fell to $31.55 a share (where he picked up $142,000 in stock). But shares have continued to fall below $30. CST’s newly independent management team aims to spruce up the company’s 1,900 gas stations. It has the resources to make that happen: Valero left CST with more than $400 million in cash to work with.

4. Phillip Morris (NYSE: PM )

After shares of this tobacco giant pulled back from the mid-$90s in the spring to $89 by early August, director Graham Mackay thought he spotted value, plunking down more than $1.1 million of his money to buy shares. He should have waited, as shares have since fallen below $84.

5. Swift Energy (NYSE: SFY )

Roughly six months ago, I profiled three companies with heavy insider buying. Although shares of Boulder Brands (Nasdaq: BDBD) are up more than 60% since then, Home Loan Servicing (Nasdaq: HLSS) has merely treaded water while Swift Energy has continued its downward ascent. Though insiders at Swift loaded up on shares at prices just under $15 in the late winter, Chairman Terry Swift took advantage of a subsequent swoon this summer to buy 20,000 shares at just $11.85 apiece. He could’ve waited a bit longer, as shares are now closer to the $11 mark. Swift has key operations in the highly productive Eagle Ford shale region, and though investors have been spooked by a recent rise in the debt load, the drilling trends are promising. Management notes that compared with a few quarters ago, the Eagle Ford wells are producing higher output at lower cost. “Most of the production impact from this additional activity will be felt in 2014 and will support a lower risk production risk profile in the future,” Terry Swift said on a call with analysts. Will this most recent insider buying finally signal a floor in the stock?

6. Calamos Asset Management (Nasdaq: CLMS )

This asset manager’s founder and CEO, John Calamos Sr., is a bit vexed right now. As I noted six weeks ago, he had been aggressively buying company stock. He kept doing so in late July and early August, buying more than $1 million more in stock at prices in the $10.50 to $10.75 range. Yet the market pullback has pushed this stock down below $10. Calamos is in the process of shifting resources away from poorly performing funds and toward higher-performing ones. Recent signs are promising, though it appears as though the firm’s founder is the only believer in this turnaround thus far.

Risks to Consider: Insiders are notoriously poor market timers, and it is best to profit from their views by having a longer-term time horizon.

Action to Take –> If the market tumbles yet lower, then you’ll need to increase your monitoring of insider activity. Insiders can help investors to see which stocks have been mistakenly dumped when a broad-based rout sets in.

P.S. — As Phillip Morris’ director knows, the tobacco giant is a bargain during its current pullback. That’s because PM is a member of a special group of securities we call “Forever Stocks.” These are world-dominating companies that pay investors a fat dividend, dig a deep moat around their business to fend off competitors and buy back massive amounts of stock, boosting the value for the rest of the shares. They’re stocks solid enough to buy, forget about and hold — forever. To learn more about these stocks — including some of their names and ticker symbols — click here.