The good times on Wall Street could be just beginning according to a reliable and rare market indicator. The Zweig Breadth Thrust indicator on Friday flashed a buy signal for only the 18th time since 1945, Carson Group chief market strategist Ryan Detrick highlighted in a post on the social media platform X. When this happens, the S & P 500 averages a 23.3% gain over the following 12 months and is up 100% of the time, history shows. The gauge — a ratio developed by legendary investor Marty Zweig — is used to determine market momentum, particularly the start of a potential move higher. The signal is triggered when the ZBT rises from less than 0.4 to more than 0.615 within 10 days. The thrust is calculated by: Determining the ratio of advancing New York Stock Exchange-listed names to the total number of rising and declining issues Then finding the 10-day exponential moving average of that ratio “Very simply, it’s when you go from very oversold to very overbought in less than two weeks,” Detrick told CNBC Pro. “That historically tends to happen at an inflection point for markets.” This buy signal came as the S & P 500 wrapped up its biggest weekly gain of the year. The benchmark index rallied 5.9% last week, marking its largest one-week surge since November 2022. That move followed the Federal Reserve hinting it may be done raising rates. “The fact that the Fed is likely done, and the fact that the economy is more normalizing than going straight into a recession are very important,” he said. But this technical signal tends to suggest “there is a lot more buying pressure coming in — which probably means an end-of-year rally is still quite likely.” Detrick thinks the S & P 500 can end 2023 between 4,600 and 4,700. That implies upside of 5.5% to 7.8% from Friday’s close. It also means the benchmark index would close out the year up 19.8% or 22.4%. To be sure, the Zweig Breadth Thrust is only one indicator, and the market could be impacted by a myriad of factors before year-end.