During volatile trading days with conflicting signals, investors need "some sort of totem that can help point us in the right direction," said CNBC's Jim Cramer.

The "Mad Money" host suggests that investors look out for large insider buying.

While insiders sell for all kinds of reasons, they only buy for one reason: "to make money," Cramer said.

Five IBM board members recently bought shares in the company, including CEO Ginni Rometty who purchased over $3 million worth of stock. Rometty's purchase, her first on the open market, signals "a real commitment," Cramer said.

IBM shares rose on the news early Monday, reversing some of last week's losses when the stock fell 7 percent after IBM announced it was acquiring Red Hat for $34 billion.

"I think the Red Hat acquisition was actually a bold move," the "Mad Money" host said. I wouldn't shun this combination just because the cloud stocks have suddenly fallen out of favor."

In 2016, J.P. Morgan CEO Jamie Dimon bought $26 million worth of stock at $53 per share. Today, the stock is more than double that price.

Corporate buybacks, like the recent activity at Berkshire Hathaway and Apple, can also signal that executives think the stock is cheap.

However, Cramer cautions that insider buying isn't always a sign that the stock is about to rally.

GE CEO Larry Culp, who just stepped into the role Oct. 1, bought over $2 million worth of stock last week. But the company "still has a ton of problems," Cramer said, including its struggling power business and ongoing restructuring plan.

Cramer's bottom line? "It's always worth taking these large insider buys seriously," although they don't always mean the stock is a buy.

Disclosure: Cramer's charitable trust owns shares of J.P. Morgan and Apple.