Possibly "Notch Defense Force", based on a Google search. My favorite go-to for this kind of question, http://www.acronymfinder.com/ http://www.acronymfinder.co

Possibly "Notch Defense Force", based on a Google search. My favorite go-to for this kind of question, http://www.acronymfinder.com/ http://www.acronymfinder.com/ , was sadly unhelpful.