According to the Economist, one accurate measure of past recessions is the number of times the news media includes the term "Recession." And guess what's happened to the number of times you can find "Recession" in print in the US lately? See this link for more.
(There's actually a formal name for counting the number of times a particular word appears in print, and using this frequency as an explanatory variable. It's called "Textual Analysis" or "Content Analysis.")