Think the weakening auto sales trend in the United States is an omen of unpleasant things to come, economically speaking? If so, then investors may want to slice the numbers in a way the media isn’t — car sales are still trending bullishly by most measures, even if nobody’s talking about it.

Take last month’s total car sales as an example. The media correctly pointed out September’s U.S. unit sales rolled in much stronger than September 2009’s total, simply because the “Cash for Clunkers” program in August of 2009 undercut the following month’s potential. All told, 949,907 automobiles were purchased in the United States last month, versus only 738,285 during the prior September’s post-“cash for clunkers” environment.

Most investors understood the bar was set rather low and understandably yawned at the numbers. After all, September’s sales weren’t even as brisk at the August 2010 total of 988,559 — suggesting the auto market is becoming sluggish again.

The problem is, that’s not the case at all.

Comparing U.S. auto sales in the full third quarter of 2009 (which encompasses “cash for clunkers” as well as the following month’s lull) to 2010’s third quarter numbers, total vehicle sales were only down about -4.4%. That’s not bad, given the artificially-induced comparable from a year ago.

That’s not the only way to examine the numbers and come up with optimistic conclusions, though. For example, year-to-date sales of autos in the United States are up by more than +10%. In fact, with only one exception, each month’s year-over-year sales in 2010 have been flat or better than 2009’s same month. The one exception was the August month comparison, of course.

To be fair, strong fleet sales have helped. Fleet sales don’t account for the bulk of the improvement, though.

So why the pessimism on the industry’s stocks? In simplest terms, though hearts and minds may be certain that car sales are going to be a victim of the “looming double-dip recession,” the numbers have persistently begged to differ. And as is usually the case, some companies have done better than others at capitalizing on this growth.

Ford (NYSE: F) is one of the obvious ways to step into the obscured auto sales growth trend. More importantly, it’s a smart way to do so, even if many feel the stock has more than reached its maximum upside.

Critics who have said there’s no possible way the auto market can continue to supply the earnings growth Ford has been enjoying have missed out on six straight quarterly earnings ‘beats’ — the last four of which were all positive earnings and the first after a nasty five quarter stretch of losses. And, with a trailing price-to-earnings ratio (P/E) of about 7.1, it’s not like the projected one of 7.2 isn’t plausible.

Even more impressive for Ford is the recapture of U.S. market share since last year, from 2009’s 16.1% to 2010’s year-to-date market share of 16.8%.

That said, only one other car manufacturer has been as impressive as Ford has in terms of market share growth — Nissan (NSANY.PK). Year-to-date, its U.S. auto sales make up 7.9% of the market’s total, compared to 2009’s total market share of 7.4%. The numbers themselves are small, but on a relative growth basis, they’re huge.

And what of Chrysler and General Motors, neither of which are publicly traded now, but both of which have initial public offerings (IPOs) in the pipeline?

Chrysler is the only carmaker that’s outpaced Nissan’s U.S. market share growth — it’s grown by +7.8%. GM actually hasn’t done much in the way of results that one of its competitors hasn’t done better. And while that’s a plus for Chrysler and a minus for General Motors when the public offerings are rolled out, it’s still too soon to pass judgment on either — the IPO documents should give investors a better idea of how to value each stock. [Read: This Hot IPO is Headed for Trouble]

On the losing end of the sales growth scale are two unlikely names: Toyota (NYSE: TM) and Honda Motors (NYSE: HMC).

All things considered, Toyota’s recall-mania from earlier in the year could have been more problematic than it was. Though the company lost market share — with a P/E in the high teens — that setback seems to be figured into the share price. As for Honda, it doesn’t even have the luxury of an excuse: though sales are technically up, the improvement is paper thin and market share is down.

On the other hand, Honda’s shares are in a strong uptrend, at least partially fueled by this year’s projected P/E of 16.6, and with a nice earnings increase expected for next year.

Regardless, the overarching reality is clear when looking beyond the anecdotal, month-to-month numbers: car sales are still improving, even if it’s hard to believe. And, the same sales growth evident in the United States is equally evident outside the country.

Action to Take –> While Ford may feel a little obvious (the “too good to be true” syndrome), it really is one of those long-term opportunities that can be taken at face value. Its stability and domestic nature can be rounded out by adding Nissan to the mix — an overseas manufacturer that doesn’t garner nearly as much attention as rivals Toyota and Honda, but should, based on its strong market penetration.

While the prospect of IPOs from General Motors and Chrysler is drawing a crowd, it may be best to steer clear. Preliminary evaluations of both IPOs suggest a lukewarm response is in store. Moreover, given the lack of supporting numbers for those would-be stocks, jockeying to own those new shares is a coin-toss proposition at best.