The silver lining is that you don't need to be a therapist to help someone in need. Many people do not show any signs or may show signs different from the norm. So it's not about having a checklist, but rather I believe it's more about being aware that we are all capable of doing it.
Suicide doesn't hit home for most of us until someone we personally know commits suicide. It's one of those things that are out of sight, out of mind. And I don't blame anyone for feeling this way because suicide sucks. The aftermath really sucks. So I hope you never experience it first hand, but even without experiencing for yourself, you can still make yourself aware. Be aware that when you ask someone if they feel suicidal, it's actually helpful to them. Be aware that talking about suicide does not make it happen. Be aware that judging someone for feeling suicidal does not make you immune from feeling this yourself. Be aware that when you have a gut feeling that someone might hurt him/herself, it's ok to be there for them even if you turn out wrong. Be aware that suicide is not the problem, it's the only solution that person sees for him/herself when he/she sees no other option.
I admit that I don't know if there is a way to get rid of suicide altogether. We can't predict what people will do and we can't control their minds or actions. We can only equip ourselves with the acknowledgement that suicide is painful and it
can, at any point, affect any of us.