Thus, this chart could provide a stark warning that stock prices are being driven more by investor optimism than the underlying value of these stocks, exactly the kind of market condition that Buffett has said makes him keep his "elephant gun" of cash at the ready.

Berkshire Hathaway’s (BRK.B) fourth-quarter 13F filing revealed that Warren Buffett continued his selling spree in the final quarter of the year. Based on the trades in Q4, the conglomerate’s cash pile looks set to have hit yet another record high after rising to $325 billion at the end of Q3.

While Warren Buffett has been building cash reserves, the rest of the market has taken their cash holdings to the lowest level in 15 years.