Hulbert Financial Digest’s Mark Hulbert says he’s seeing extreme pessimism among newsletter editors he tracks — and that may bode well for the market.

”I’ve seen perhaps one of the fastest trips from the bull side to the bearish side among the advisors that I track that I’ve seen in years,” Hulbert tells CNBC, “and that’s an encouraging sign. You hear the old saying that the time to buy is when the blood is running in the street, and believe me the blood is running.”

The newsletters Hulbert tracks are on average recommending a mere 20% exposure to equities. That sort of sentiment may be a contrarian indicator, he says. He notes that in late April, some of his sentiment indicators showed there was as much bullishness among advisors as he’d seen in a decade — and that preceded the market’s recent decline. Now, the opposite may be happening, with the high negative sentiment presaging a turn for the better, as has often happened throughout history.