The cardinals themselves are not a sign of spring because they live here year-round. But when they start singing! we know spring is coming, if not immediately, then further on down the road.... When the sun warms up and the daylight extends, they know! And they have been singing up a storm lately, despite today's very cold weather. (This is a photo from a few years back).

To see others posting their signs of seasonal change: https://forum.pbase.com/viewtopic.php?f=16&t=48985&sid=0282605a6faac67a09fac18b4a95838e