Top executives at big companies known as corporate insiders bought back shares of their own firms' stock at the second lowest rate in at least two years last month, even as speculators continued to buy the dip.Why it matters: Insiders are typically bullish on their own company and buy when prices fall, but declined to do so after all three major U.S. stock indexes fell by at least 2% during the month, the second consecutive month of declines. (The Dow fell 6%, its worst monthly showing since March's historic drop.)What happened: Insiders were big buyers in March as the Fed stepped in with its QEinfinity program, correctly timing the selloff's bottom, but were largely absent in October. Fewer than 380 corporate executives and officers bought their companies' shares, according to data compiled by the Washington Service.They bought $74.3 million worth of shares in October, down 43% from September, according to SEC filings compiled by Bloomberg.Selling by the group dropped 29% to $1.67 billion.What it means: “What they’re telling you is, 'Our stock is not cheap and maybe expensive so it doesn’t make sense for us to buy the dip,'” Malcolm Polley, president and chief investment officer at Stewart Capital Advisors, told Bloomberg.“While earnings have certainly improved versus Q2, the rate of improvement going into Q4 and Q1 of next year will probably slow pretty dramatically.”Between the lines: Companies' buybacks are rising from the second quarter's big dropoff but remain well below 2019's pace, suggesting U.S. corporations are in no rush to buy back their shares either.S&P 500 companies bought back $199 billion of their own stock in the first quarter, but that figure dropped to $89 billion in the second quarter, a more than 50% reduction, according to data from Goldman Sachs.In the third quarter, Goldman estimates companies bought back $112 billion and will buy back $125 billion in the fourth quarter.Yes, but: Most of Wall Street remains generally bullish on the stock market, especially large speculators, who have boosted their net positions in S&P 500 e-mini futures to the highest level since January 2019. And the low levels of buybacks from insiders could simply be a sign of unease ahead of the U.S. presidential election.Futures contracts on expected volatility continue to show traders pricing in extremely high risk associated with today's election.Data from the Investment Company Institute show investors are still holding $4.35 trillion in money market funds, essentially cash, which is more than the highest level ever held prior to 2020.The big picture: Companies' lack of stock buying could be another negative sign for stock market fundamentals. Stock buybacks accounted for about half of the earnings growth for companies in 2018 and essentially all of it in 2019.Overall earnings for S&P companies are expected to be negative every quarter this year compared to 2019, and stock prices are more than 10% above where they were a year ago, with historically extended price-to-earnings ratios.Net buybacks are expected to be flat for the year, as companies have issued more shares of their stock this year, including many of the market's previous buyback leaders, Brian Reynolds, who tracks buybacks at Reynolds Strategy, told CNBC.