U.S. stocks have remained resilient this year despite rising risks, but several warning signs are appearing beneath the surface. According to Sina Finance, BTIG technical strategist Jonathan Krinsky said the ratio of declining volume to total volume on the New York Stock Exchange has surged to 54%, near this year's high on Nasdaq, while the Russell 2000 Index has fallen more than 5% from its recent peak.

Krinsky wrote that this combination has appeared only 12 times since 1996. Historical data show that S&P 500 performance after such episodes has been mixed, while the Russell 2000 has averaged a decline of about 2.1%.

Even so, the S&P 500 remains close to its record high. The index is about 3% below the all-time peak of 7,798.99 set on August 13, and is up about 11.7% year to date.

Truist Chief Investment Officer Keith Lerner said investors with underweight allocations could consider increasing equity exposure, and that growth sectors such as technology currently offer relative opportunities. He added that if the market sees a deeper pullback, investors could consider adding more aggressive positions.