A pursuivant is a junior officer of arms. In England, pursuivants in ordinary take their titles from symbols of the monarchy. Pursuivants extraordinary take their titles from symbols of the Duke of Norfolk, who nominates them. In the case of Rouge Dragon Pursuivant in England, or Unicorn Pursuivant in Scotland, the title is a mythical, heraldic beast.
So what better title for a self-appointed herald from the American west than Jackalope Pursuivant?