Here's a couple things to look for. Not just on a post but also any other interaction. ,(Typically when someone says on social media "Im going to kill myself" its an attempt to get people to be sympathetic snd.)

If someone starts giving away possessions, expressing gratitude to loved ones AND its out of nowhere, starts acting as if no matter how severe something is that should normally be viewed as serious they brush it off (they know in a shirt time they wont be alive so why deal with it).. also sometimes people planning to hurt themselves will start having personal convos with specific loved ones thanking them, etc. Some people will go from visably depressed for a long time prior to planning, and flip to appearing way happy or enjoying life.

Just be cognizant thst when u already know a person is struggling eith depression, if they start having a heart to heart type convo and with more than 1 person--just cut to the chase and ask the hard question but in person

As sad as it is to say, more often than not the individuals who are selfish eniugh to take their own life dont say anything to anyone once they decide. They just do it. So most people who talk about it or start doing some of the things i mentioned are either afraid to follow through (thankfully) or its more of a fishing for sympathy attempt. But doth can get eventually turn into a serious attempt to hurt themself

Yhe more u can help a person while being physically present the better. A FB message of love snd hope doesn't do much but saying it to their face does