What was the Saints signature win in 2017/18?

Not Washington. That was a mediocre team who had lost Chris Thompson early in the game.
Not Buffalo. It's Buffalo.

I would first go with beating Carolina in the playoffs. The way we held them off at the end and completed the 3-game sweep was most impressive. The coach and players let us know what a signature win it was with the broom dance.

Close behind is the Falcons game, which had so much riding on the line for the division title. The Ginn TD before halftime and then the goal-line stand in the 2nd half were signature-esque.