So yea, suicide is a huge fucking issue in online communities, and I'm kind of embarrassed that I've never thought of it before when it comes to this site. I'm not sure if this is official or anything, but these are the guidelines I have when I see someone threaten or suggest suicide:
1- Remember that we are not mental health professionals, and this isn't a mental health community, so posts where people clearly need outside help will be removed.
2- After you remove a post, send the poster something like this:
If you feel you might be suicidal, and live in the United States, I urge you to call the Suicide Hotline at 800-273-8255 or navigate to http://www.suicidepreventionlifeline.org/ for a live chat and additional resources.
If you do not live in the United States please seek out local resources. Let me know if you need any other guidance to resources.
They may respond with the country they live in, if so you may be able to figure out resources for that country. But remember, only point to resources, you do not need to give them detailed advice or personal experiences.
3- Do not link to other subreddits or online communities, as that may make them targets for trolling. If it feels appropriate, message admins, even on a bad site like reddit.
Like I said, these aren't official, but it's something that I wanted to put out in the open and this seemed like the most appropriate place to talk about it.
As a side note, I looked up what reddit admins suggest in these cases, and they actually say "link to r suicidehelp" which is like, what the fuck? r suicidehelp is good as these things go but it's a massive trolling target, as are all public mental health forums. I'm pretty sure that reddit admins can't see anything a step beyond what's in front of their face.
Edit: I was also pointed to Trans Lifeline, which is a good resource to know.