The eeriest reason you should be wary of a pullback in October is the similarity between the chart of the rally that began March 9 and the 1937-1938 rally, which was followed by a sharp pullback.

They are practically identical -- seriously, check it out.

This could be a harbinger of a major slide beginning no later than December, but probably starting in October.

Two key elements of the market's rise -- short-sellers covering their positions and money managers looking for quick profits -- are waning, reducing buy-side volume.

This will eventually impair the market's ability to sustain itself as more shorts are entering the market and more managers are preparing to bank profits before the end of their year on Nov. 1.

Next: Sign #10: An eerie similarity

Market volume is so light that many technicians do not see the rise in the indices as "real." They want to see increased buying volume to confirm another upward leg in the rally.

While volume may increase in the short term, it still will be considered light, as many investors are very cautious (and should be) about getting in after a 40% rise in the markets. Without heavier volume, the market is very vulnerable to a downturn.

Next: Sign #9: Short covering and money managers looking to bank profits

The market has been indiscriminate in this rally, pushing up 487 out of 500 S&P stocks. This level of irrationality is ending, and certain segments are going to take a hit.

Once this happens, the broad-based support for the S&P 500 will erode brick by brick.

Next: Sign #8: Light volume

Now that we've covered a few of the fundamental reasons the market is likely headed down in October, let's turn to some of the technical reasons.

First, the market is overbought by almost historical norms. And the rally, which began March 9, is having more and more trouble piercing technical ceilings.

Major resistance levels are 1,045, 1,075 and 1,110 on the S&P 500. And a major failure at one of these levels could be a tip-off that the slide has begun.

Next: Sign #7: An indiscriminate rally

The market is radically overvalued based on current earnings. Historical norms say the S&P 500 should be at 850, not 1,065.

And the depressed economy will lead to depressed earnings next year, which means the market will be even more overvalued than it is at current levels.

This will be made clear with October earnings announcements.

The current drivers of the market -- commodity speculation, green shoots euphoria, and enthusiasm over China thanks to fabricated Chinese economic data -- will be played out in the next few weeks.

Absent these drivers, there are no positive catalysts left to underpin a rising market.

Next: Sign #5: Earnings will disappoint

The banks led the markets down, and then led it back up. And when they announce earnings in October, they are almost positively going to include comments about 2010 that will help send the market back down.

The banks still have trillions of dollars in toxic assets and increasing credit losses, and they are facing new accounting and regulatory rules that are pressuring them to raise capital and dilute shareholders.

And the market is not likely to react well to this news.

Next: Sign #4: No positive catalysts on the horizon

Without consumer spending picking up drastically, the economy is facing a W-shaped recession/recovery -- not a V-shaped one.

We are currently climbing the second leg of W due to rising expectations about the economy. But the economy is not improving -- it is just not declining as fast as it was.

This realization will likely hit Wall Street next month, sending the market back down.

Next: Sign #3: The banks will lead us down again

The driver of the U.S. economy is the consumer -- consumer spending accounts for 70% of the nation's GDP -- and the consumer is down and out.

Americans have lost 40% of their wealth in the past two years; more than $4 trillion in credit lines will have vanished by year-end; the real unemployment rate (unemployed, discouraged and part-time workers wanting full-time work) is roughly 20%; and weekly work hours and wages are stagnant. In short, most consumers have no extra income to spend.

Next: Sign #2: W-shaped recession

The talk of the financial town right now is how the market has entered into a recovery period. Gives you a nice, toasty feeling, doesn't it?

Well, not so fast. October is a historically temperamental time on Wall Street and, while some people believe the market is going to keep climbing higher, others are terrified it will sink like a stone.

If I were a betting man, I'd say the market will likely crash in October. What makes me say that? Here are five technical and five fundamental reasons to back it up.