Are there ways of detecting them?
Like, do they use certain words or ask certain questions which should raise alarm bells?
I ask because sometimes it can be hard to tell when someone is asking certain questions because they want to make sure another member has considered all their options, and when someone is trying to be intentionally disruptive, sow doubt, create fear about ctb etc.
To me they're pretty obvious. It's not only a matter of asking if someone has considered all their options, they usually add additional persuasive, obviously pro-life rhetoric.
When the waves happen, there are usually two to three new members who will try to talk someone out of suicide. They often target younger members. Sometimes they will have a username or signature that's blatantly obvious, like something to do with victory or life being wonderful.
There was one member, Morticia'sHair, who started out with a lot of love-bombing, leaving notes on profiles and lots of caring comments, lots of heart emohis everywhere. Then after a few days, maybe a week (?), she and another new member tried to stop a couple of younger members on their goodbye threads. She acted very loving as she'd bring up the members' parents, and then would follow up with guilt trips. She was a member for only a week or two, and some members were upset she was banned because she was so sweet to them. She had some suspicious posts, and then got overt.
So some of them will try to blend in for a bit and seem supportive, and then start trying to interfere on goodbye threads. Some will just jump right in and make blatant pro-life comments on a variety of threads. Younger members get targeted. And this generally happens in a wave of about a week or a little longer, maybe an average of four pro-lifers during that period. I won't say how often the waves come because they'll just switch it up, and of course they may even switch up this pattern now that I've called it out, but I'm not too worried about it.
There are also pro-lifers who will pretend to be suicidal, befriend someone in PMs, and then when it comes time that the member wants to suicide, will blatantly try to talk them out of it, even threaten or actually call LE. I've only read about this on the forum, I don't do PMs.
You mentioned sowing doubt. That happens, too, but it's often not as overt, and I haven't yet been able to say for certain when someone is a pro-lifer. There are lots of ways for them to play games. I suspect there some have had accounts for a long time and keep a very low profile, occasionally posting quite convincingly that they're suicidal (as some of the PM targeters do), sowing doubt here and there, maybe or maybe not developing some PM relationships, then going quiet again for a while as the total membership seems to go through major shifts about every four months.
I've talked about it before on the forum when it's in progress. If you search "infiltration" with my username, you can get more information with examples.