Personally, I think the best spring indicator around is the "time to shave your legs again feeling" that all women get when they feel the first warm breeze of the season.  However, there are a few others that are near and dear to my heart.

You know it is almost spring when the kids come home from school with more mud on their snowpants than snow.

...when you start to see teachers buying earplugs...yes, they get incredibly loud between February and spring break!

...when you start to see flowers bloom but you know that in a couple of days there will be a freeze and they will be goners.

...when you start to dress in layers - not because it is cold out, but because you don't know what will happen by noon.