For over two months, I have been aware that spring is coming. The very first sign, I believe, was the noticeable lengthening of the day. By mid-January I noticed that the days were getting longer, and by the end of the month I was no longer leaving work in the dark. It marks a time when the geometric center of the Sun crosses the equator, and is visible for approximately twelve hours everywhere on the Earth. I say approximately because it is not exactly twelve as is popularly believed.
Atmospheric refraction causes the Sun to appear to rise earlier that it actually does.
Also, we mark sunrise at the time when the smallest sliver of the sun can be seen, but we mark sunset when it has finally disappeared. These factors add a few more minutes of daylight, so that the day of the equinox actually tends to be a couple of minutes longer than the night. The end of March has long been observed as a time of rebirth, new beginnings, fertility, and resurrection. The ancient Greeks divided the seasons into three periods. Spring occurred during the months when Aphrodite, goddess of love and fertility, was with her Adonis and was happy.