My personal sign is when you start seeing awkward collaborations start cropping up. One time when I was thrifting, I picked up a graphic novel that had the Justice League, team with the Power Rangers of all things. I glimpsed into what the plot was about out of morbid curiosity and it was just a plain generic time and dimension thing.
Nothing ever connected between the teams at all. DC Comics, while fledgling at times with how they go about their series and movies, still have far more relevance than Power Rangers do. I think the Power Rangers are just grasping at straws to keep being relevant when people have largely moved on from them.
I was a ready for Lost, because I remember X-Files, which was the granddaddy of bullshit plots. We all thought there was something going on with the cigarette smoking man, the dark room full of weird old men, the tar, etc. and then they admitted that they had no plan, no plot, they were just making it up as they went, none of it made any sense, and they had no idea where this was all leading. That was the end of X-Files for me, and everybody else.
So when Lost started, I got the vibe that this might be like X-Files, and I think it was, to an extent. I think they had a general idea, but they definitely hadn’t written the ending first, and made their way toward it. I figured out that they were flailing somewhere around the middle of the 3rd season and bailed. When it ended, and everybody was irritated, I knew I’d made the right choice to bounce.