My experience is that they show up when I need them. But that doesn't mean that the manifestation you want shows up. I got so many signs that my ex would come back but I had so much resistance going on that it never happened. How you already said..you can't rely on signs. When you ask for a sign without resistance then you get it, but in my opinion it has nothing to do with the actual manifestation. It is a completely independent manifestation.
I never got a sign for a big manifestation because I didn't care for signs. I knew it would come. Why looking for signs then? It's nice that seeing the sign raised your hope. Hold on to this. But in the long run it would be better if you could just KNOW that you can't fail when you do the right things. There are so many success stories on this bord lately and that's no coincidence. The people who succeed aren't just lucky or their ex just decided to take them back. They totally attracted this. You can do that too.

He can't get you out of his mind. He is totally crazy about you. If that is what you believe about him it will be your experience.