I think the figure was supposed to represent Catherine Segurane, a local, legendary heroine, who is said to have helped repulse the Turks in 1543.

But the whole thing went back to earlier rites of spring. On the hill in the background of the first photo is Nietzsche's terrace. In The Birth of Tragedy he said:

... with the potent coming of spring that penetrates all nature with joy, these Dionysian emotions awake, and as they grow in intensity everything subjective vanishes into complete self-forgetfulness.

In the German Middle Ages, too, singing and dancing crowds, ever increasing in number, whirled themselves from place to place under this same Dionysian impulse. [...]

There are some who, from obtuseness or lack of experience, turn away from such phenomena as from "folk-diseases," with contempt or pity born of consciousness of their own "healthy-mindedness." But of course such poor wretches have no idea how corpselike and ghostly their so-called "healthy-mindedness" looks when the glowing life of the Dionysian revelers roars past them.

But there was also a reminder of the more recent, political significance of May day:

"Employment Code - premeditated murder":

The duality of Nietzsche's favorite metaphors, namely the succession of waves in the sea, on the one hand, and flame, light, and fire, on the other, demonstrates this duality of his Dionysian thought in which the eternal movement of energy is wedded to the ultimate stasis of unity.

http://www.nietzschecircle.com/essayArchive3.htm