This. As someone who analyzes ad spend as part of their job I cannot imagine a scenario in which we would turn down ad spend prior to a downturn in consumer spending? If we're getting good ROAS we aren't turning off the hose.

To give OP the benefit of the doubt. Maybe what OP means is that Ad Spend is one of the first lagging indicators to show up. Consumer demand weakens, companies turn down ad spend, and then a few months later the reduction in revenue shows up in the quarterly report. So as an indicator it leads earnings reports and share price drops but lags actual consumer spending.