I agree, suicide rates are on the rise and I feel that is due to the level of trauma and violence that also seems to escalate. As for the warning signs, a search on your favorite search engine on that topic may help you. But if you are asking me what signs I was giving off, well, there were many.
To be clear, there is a huge shift when I was thinking about suicide and deciding to actually do it. Because I was in so much pain, I spent a lot of time on line looking for painless ways to kill myself. I'm sure my browser history was painted full of blunt signs of my intent. Although, most people would not have access to that. For me, I found that isolating myself was important as I did not want to tip off anybody. I worked hard to be alone. Many would talk about a sense of calm after making the decision, but for me, there was no calm. It was all secret and I worked hard to hide it. Something I suspect you can relate towards based on your comments above.
The hints were not found in what could be seen but what could not be seen or what disappeared. By walking away from family and friends, the act of isolation was the sign. So rather than watching for a red flag to pop up, watch for the red flag to disappear! It requires vigilance and persistence as most people will notice when something pops up into their field of vision. However, most people will not notice when something disappears!
I hope that helps.