Warren Buffett is telling investors something -- not through what he has said, but through his actions with the balance sheet of his investment conglomerate Berkshire Hathaway ( BRK.A -0.40%) ( BRK.B 0.83%). These actions should be taken as a warning sign with the stock market reaching elevated valuation levels in recent months.

The billionaire’s Berkshire Hathaway investment group has firmly outpaced the S&P 500 over the past five years, and has delivered staggering returns since he began converting it from a textile company into an acquisition machine in the mid-1960s.