Just noticed something pretty significant in Berkshire Hathaway's latest report that should grab investors' attention. Warren Buffett's been quietly sending a pretty loud message through his portfolio moves, and the numbers are hard to ignore.

So here's what caught my eye: Over the past 13 quarters, Berkshire has been a net seller of stocks totaling $187 billion. That's a massive shift from Buffett's historical playbook. Back in 2018, he told CNBC it was hard to imagine many months when they weren't net buyers. Now? The opposite is happening.

Sure, you could argue Berkshire's just too big to move the needle anymore with most deals. The company's tangible book value has more than doubled to around $580 billion, and they're sitting on over $300 billion in cash. They even picked up positions in UnitedHealth Group, Alphabet, and The New York Times last year. But here's the thing—even with all that dry powder, Warren Buffett and his team still sold more than they bought every single quarter.

That's not random. That's a warning signal about valuations.

The S&P 500's CAPE ratio hit 39.8 back in February, and that's a number that should make people think twice. Apart from the last few months, you'd have to go all the way back to the dot-com crash in 2000 to see readings this extreme. We're talking about a valuation level that's only shown up 26 times in the 69 years since the CAPE was created.

Here's where it gets interesting: History shows what happens when the S&P trades at these levels. According to the data, when the CAPE ratio exceeds 39, the index has averaged a 30% decline over the next three years. In the shorter term, we're looking at potential 4% drops within six months and 20% declines over two years.

Now, I get it—historical patterns aren't guarantees. AI could accelerate earnings growth faster than anyone expects, potentially justifying current valuations. But the fact that Warren Buffett is essentially sitting on the sidelines after decades of being an aggressive buyer? That's worth taking seriously.

The smart move probably looks like trimming positions you couldn't stomach holding through a nasty downturn, and if you're buying, focus on companies trading at reasonable valuations with earnings that could realistically double in five years. Warren Buffett's $187 billion in net sales is essentially his way of saying the risk-reward setup doesn't look great from here.