Many people have different definitions for the beginning of spring. For some, Imbolc is the first day of spring, for others it is spring equinox. For some, it's marked by a holiday like Easter or Spring Day. As a child, I always heard the first day of spring was the first day you saw a robin. My new family doesn't measure spring in birds; we measure it in flowers.
To me, the nails most clearly represent the actions you have to undo in order to improve a situation or undo a past fuck up. This would make them amazing for shadow work.