We can never tell what is going on in someone else's head even if we do tend to lie to ourselves and think we can read people. If someone really wants to kill themselves there is little outside of heavily supervised suicide watch we can do to prevent them.

The only way to help is to make them feel comfortable enough to ask for help and accept help that is offered. Red flags may make people feel better because they did something but that something has great potential reduce the number of willing to ask for help.