The footprint is an uncommon formation found in Stranded Deep. Footprints are non-interactable and can be found on islands.

Footprints in the sand.

The presence of footprints may mean that another person, most likely another survivor, had traversed the same area at another point in time prior to the events of the game. It is speculated that this person is the same person who had left the DeadEx Box and/or Wollie out at sea.