The ice blue scillas are in bloom at the foot of Shakespeare's Garden! That is my sure sign of spring in NYC! They are at their peak NOW so try to go as by weekend they could be just over it.
They cascade like a lawn of starry blossoms and have a light sweet scent something like honeysuckle, though it's not strong, you must seek it out downwind.
The snowdrops, early crocus, dwarf and early irises, very early tulips, jonquils and even daffodils are in bloom. The forsythia is just beginning and some of the early trees are starting to bloom as well...