A divide has formed in the US equity market.

As the investing public has continued to devour stocks, sending all three major indexes to record highs in the last few months, corporate insiders have been offloading shares to an extent not seen in seven years. Selling totaled $10 billion in March, according to data compiled by Trim Tabs.

It's a troubling trend facing an equity market that's already grappling with its loftiest valuations since the 2000 tech bubble. If the people with the deepest knowledge of a company are cashing out, why should investors keep buying at current prices?

The groundswell of insider selling has the attention of Brad Lamensdorf, portfolio manager at Ranger Alternative Management, and he doesn't like what he sees.

"This is definitely a negative sign," Lamensdorf wrote in his April newsletter. "They do not see value in their own companies!"

One possible explanation is that insiders have been unable to resist the allure of collecting profits with many of their stocks trading at unprecedented levels. Still, that begs the question of why a person would do that if they were at all confident that shares would continue to rise. No matter how you slice it, it's a bad sign for the average investor.

In addition to high valuations, Lamensdorf cites rising rates as a risk facing the stock market. As the Federal Reserve continues hiking, an increasing number of companies will be unable to meet interest payments, exposing them to default, he says. As such, his portfolio is 50% net short.

Not all market experts are as pessimistic.

Wall Street strategists see the S&P 500 grinding 1.5% higher from Monday's close through year-end, according to a 19-person survey conducted by Bloomberg.