The other day, we were coming up with a few simple rules to use for screening stocks. One of them was this: If a company has more than one page of Form 4s on the SEC's filings database, you should be very wary -- unless they're all insider buys.

Seen Google's (NASDAQ:GOOG) SEC file lately? It's almost nothing but Form 4s. I stopped looking after 320 entries, or four pages' worth. Among the highlights: $230 million worth of sales by each of the founders, Larry Page and Sergey Brin, in the last couple of months alone. CEO Eric Schmidt also sold shares worth tens of millions. But here's the thing: These sales represent very small portions of the millions of shares they hold. How can $240 million be a single-digit percentage of one guy's Google stake? The company's worth nearly $90 billion, that's how. It's simply mind-boggling.

And who could blame them for lightening the load? We already knew that Google was trading at pretty rich prices. Google itself admitted as much when it sold $4 billion worth in a follow-on offering just weeks back. No one does that when the stock is cheap. Smart management does that when the stock is hot.

What's this mean? You'll have to decide that for yourself. One thing's for sure. Google has made plenty of people rich, both insiders and those who bought at the IPO. Whether the shares continue to defy gravity from here is another question. It seems to me that insiders are betting that it's less likely, at least for the immediate future.

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Seth Jayson had trouble enough contemplating the googol. At the time of publication, he had no position in any company mentioned here. View his stock holdings and Fool profile here. Fool rules are here.