A Noticeable Penis Line is the outline of a guys penis in pants (especially gray Sweatpants). The Noticeable Penis Line is usually there when a guy isn't erect and indicates weather or not he'd be good in bed. Also referred to as a NPL or Perpindickular Peen Scene.
Person 1: hey did you see Chad's NPL?
Person 2: his what?
Person 1: his Noticeable Penis Line, lemme just say it's not very Noticeable.
Person 2: no it isn't is it. But look at brad in those gray Sweatpants
Person 1: Damnnn I'm straight but he makes me wanna switch sides just as bad as Ryan Reynolds.