The biggest trouble sign for stocks may be bonds.
High-yield bonds, specifically, often are seen as an effective proxy for movements in the equity market. If that's the case, trends in junk are pointing to a rocky road ahead.
Average yields for low-rated companies have jumped to 7.3 percent and spreads between such debt and comparable duration Treasurys have widened dramatically, according to David Rosenberg, chief economist and strategist at Gluskin Sheff.
History suggests that fallout in stocks is not far behind.
"If you think the equity market is heading for a spot of trouble here, the high-yield bond market is having a coronary," Rosenberg said in his daily market analysis Thursday.
Rosenberg points out that the average yield is the highest since mid-December and has risen 120 basis points—1.2 percentage points—just since June. Spreads are at 580 basis points, a level hit only twice in the last three years. His caution on junk reflects sentiment heard from a number of other market analysts who believe the troubles in the high-yield market, which has led fixed income performance with 7 percent annualized returns over the past 10 years, are a bad sign.
Since the most recent lows in June, spreads have widened a full percentage point.
"In other words, this move in high-yield spreads is on par with what we have seen when we have previously had a 9 percent correction in equities or what would be about the same as the S&P 500 now correcting to 1,910," he said.
"Yet the stock market is off just over 2 percent (during the most recent selloff) so either the S&P 500 has more downside from here or spreads are going to have to adjust by tightening back in," Rosenberg added.
For the year, the is up 1.5 percent though it has fallen nearly 1 percent over the past month and has spent the year locked within a tight range, never finding a solid direction to either side of breakeven.
Read More'No value left' in high yield market
Retail investors have been yanking money from U.S.-focused mutual funds, which have seen $155 billion in outflows over the past 12 months, according to Morningstar. Passively managed exchange-traded funds have seen almost the same amount of inflows, but ETF players have been running from junk.
The fund has seen $529.5 million in outflows over the past week and $2.07 billion since June 1, while the SPDR Barclays High Yield Bond ETF has had respective outflows of $307.6 million and $1.36 billion in the same time frames, according to ETF.com.
The Barclays High-Yield Corporate Composite Index is up about 2.3 percent year to date but off 1.3 percent over the past three months. The above-mentioned ETFs have seen respective declines of 3.1 percent and 3.7 percent over the three-month period.
Rosenberg said he remains longer-term bullish on the market, based in part on subdued investor sentiment. This week's American Association of Individual Investors survey, released Thursday, shows bullish investors—those expecting the market to be higher in the next six months—at just 30.5 percent, with the bears at 36.1 percent.
"Excuse me if I point out that bull markets never end with this level of negative sentiment," he said.
Still, Rosenberg pointed out that multiple S&P 500 sectors already are in corrective phases from their most recent highs.
"If there is downside now, it is more in the equity market than it is in the credit market," he said, but advised "be cautious near term but with an eye to buy because the dust in corrective phases tends to settle in a matter of weeks or months."