It's not the vernal equinox. It's not the warmer weather. It's not the flowers blooming. It's not the asparagus, peas, or strawberries showing up at the farmer's market. Heck, it's not even the fava beans at the farmer's market.
For me, spring doesn't officially start until the day the Fava Bean Crostini with Pecorino Cheese and Truffle Oil reappears on the menu at Bacco. That day was yesterday. I haven't yet eaten them, but you can bet I will very soon.