Well, in general a trigger icon is a good idea if:

- You're discussing thoughts of harming yourself, or self injury
- You're discussing abuse or abusive situations

- You're discussing something that you, yourself, would find triggering - but basically it's stuff that might cause someone else to be very triggered. Granted we cannot account for everyone's triggers (like if someone was triggered by "blue" for instance) but we can account for the most common ones.

When in doubt, you can add a trigger icon. Otherwise if you don't think a post warrants a trigger icon, don't put one on. If we get a request to put one on, we'll do it, or if I come across a post that I think might need one, I put one on. (I never remove a trigger icon from a post because if a member puts one on I've decided they think it needs one).