It's interesting, actually, that you bring it up. I just now discovered I've been witnessing a "red flag" situation from the outside without realizing it.
Here on the forum, I share the story of my scientologist friend whom I'm worried about, and according to what I told before, she has a scientologist mother and yet her choice of becoming one herself wasn't obvious.
I thought she left everything abruptly and flew abroad to join the church. But as it turns out, when she flew abroad she was already "Clear", and the last time I saw her she was on her way to get there. I didn't know that then, and yet she projected something that made me feel strangely alramed. There was a strangeness about her, no doubt a result of hours of auditing and training. Anyway, it drove me nuts that no one else noticed it, that was seriously "red flagged" time..on my part.
Since my friend joined (currently she's has some OT level..), I myself became way more sensitive and careful when it comes to organizations and self-help books and courses. I'm pretty sure that before all this has happened and got me to fully investigate scientology, I was naive, and it would took me quite a while to sense that something might be wrong.
Nowadays, it's like
"Please sign a petition against Ritalin"
-danger!-
"We can help you reprogram yourself, and clean the present from bad momories"
-danger!-
"Learn fascinating ways to get in touch with your spiritual self"
-danger!-
Here's to Red Flags!

We should use this slogan in front of Flag's building in Florida(;