As regular Daily Ticker viewers will know, I have recently become concerned about the possibility of a stock-market crash — or, at the very least, a long period of crappy stock returns.

Importantly, I'm not predicting a crash, but I think the odds of one are increasing. And I am holding onto my own stocks only because I have a balanced portfolio and a long-enough investment horizon that I am comfortable with the possibility of stocks plunging, say, 50%, over the next year or two.

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Of course, stocks have done so well over the past five years that almost everyone is bullish these days, so whenever I talk about the possibility of a market crash, people cackle with laughter or dismiss me as a hater, shortseller, or moron.

For what it's worth, I'm not short stocks. I'm very long. I hope stocks continue to charge higher, but I just can't find much valid data to suggest that they will. I only have vague hopes that the Fed will continue to pump air into the market balloon, the U.S. economy will finally start cranking again, and corporations will continue to find ways to cut more costs and grow their already record-high profit margins and earnings.

Meanwhile:

• Every valid valuation measure I look at suggests that stocks are at least 40% overvalued

• Corporate profit margins look like they might finally be rolling over

• Lots of sentiment indicators are flashing ever-brighter warning signs

None of this means that stocks will crash. But, the valuation data, at least, does suggest that, at best, stocks are likely to produce lousy returns over the next 10 years (0%-2% per year, including dividends).

I'll describe these issues in detail below. Before I do, though, I want to stress that I am not giving you investment advice. I know nothing about your personal investment goals, risk tolerance, or time horizon, and without that information, I have no idea what you should do with your portfolio. (I'm also not allowed to give you investment advice, but that's a different story).

What I do think you should do is ask yourself, "If stocks dropped 50% over the next two years, would I be comfortable with that?" If your answer is "no" — if a drop of that magnitude would cause you to lose sleep or panic and sell — then I would respectfully suggest that you consider rebalancing your portfolio. Not selling all of your stocks — for many reasons, that would almost certainly be dumb. Just rebalancing.

Okay, which valuation measures suggest the stock market is very overvalued?

These, among others: