Peepers

Last night on my way home from knit night I heard marsh peepers. They were singing loud and clear and I heard them even with the windows closed. There's one particular area that has a concentrated population. This is where I hear them while on the road. I always think Spring is just around the corner when I hear them. I've been proven wrong and we've had freezes afterward but, to me, it's still the first real sign of Spring.
What's the first real sign of Spring to you?